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Wisconsin  Geol.  and  Nat.  Hist.  Survey. 


Bulletin  No.  XXV,  Plate  I. 


B.  Up-curve!  in  beds  of  the  Chequamegon  sandstone,  east  side  of  Outer  Island. 
These  phenomena  may  be  <lue  either  to  folding,  concretionary  iron  banding,  or 
original  deposition  (see  p.  30). 


Wisconsin  Geological  and  Natural  History  Survey 

E.  A.  BIRGE,  Director  W.  O.  HOTCHKISS,  State  Geologist 


BULLETIN  NO.  XXV 


SCIENTIFIC  SERIES  NO.  8 


SANDSTONES  OF  THE  WISCONSIN 
COAST  OF  LAKE  SUPERIOR 


FREDRIK  TURVILLE  THWAITES 

Curator  of  Geological  Museum 
University  of  YTuconsin 


MADISON,  WIS. 

PUBLISHED   BY   THE  STATE 
1912 


ORGANIZATION  OF  SUKVEY 


BOARD  OF  COMMISSIONERS 

FRANCIS  E.  McGOVERN 

Governor  of  the  State. 
CHARLES  R.  VAN  HISE,  President 

President  of  the  University  of  Wisconsin. 
CHARLES  P.  CARY,  Vice-President 

State  Superintendent  of  Public  Instruction. 
JABE  ALFORD 

President  of  the  Commissioners  of  Fisheries. 
DANA  C.  MUNRO,  Secretary 

President  of  the  Wisconsin  Academy  of  Sciences,  Arts,  and  Letters. 


STAFF  OF  THE  SURVEY 

ADMINISTRATION: 

Edward  A.   Birge,  Director    and  Superintendent.    In  immediate 

charge  of  Natural  History  Division. 
William  O.  Hotchktss,  State  Geologist,    In  immediate  charge  of 

Geology  Division. 
Bess  C.  Brewer,  Clerk. 

GEOLOGY  DIVISION: 

William  O.  Hotchkiss.    State  Geologist, 

T.  C.  Chamberlin.    Consulting  Geologist,  Pleistocene  Geology. 

Samuel  Weidman.    In  charge,  Areal  Geology. 

Edwin  Steidtmann.    Assistant,  Geology. 

F.  T.  Thwaites.    Assistant,  Geology. 

R.  H.  Whitbeck.    Assistant,  Physical  Geography. 

Lawrence  Martin.    Assistant,  Physical  Geography. 

V.  C.  Finch.    Assistant,  Physical  Geography. 

NATURAL  HISTORY  DIVISION: 
Edward  A.  Birge.    In  charge. 
Chancey  Juday.    Lake  Survey. 
George  Wagner.    Report  on  Fish. 
Louis  G.  Steck.    Assistant,  Lake  Survey. 

DIVISION  OF  SOILS: 

A.  R.  Whitson.    In  charge. 

F.  L.  Musback.    Field  Assistant  and  Analyst. 

Guy  Conrey.  Analyst, 

E.  J.  Graul.    Analyst  and  Field  Assistant. 

T.  J.  Dunnewald.    Field  Assistant  and  Analyst. 

C.  Thompson.    Field  Assistant, 

O.  J.  Noer.    Field  Assistant. 

A.  L.  Buser.    Field  Assistant. 


14C 


TABLE  OF  CONTENTS 


Introduction 

Purpose  of  the  Investigation 
Summary  of  Results 
Method  of  Field  Work 
Maps 

Acknowledgments  . 
Expedition  of  1912  . 


Page 
1 
1 
1 
3 
3 
4 
5 


Chapter  I — The  Topography  of  the  Wisconsin  Coast  of  Lake 
Superior 
General  Statement  . 
The  Southern  Highland 
The  Trap  Ranges  :  Douglas  County 
North  Range 
The  Bayfield  Ridge  . 
The  Apostle  Islands 
The  Western  Plain  . 
The  Eastern  Plain  . 
Outline  of  Surficial  Geology 


Chapter  II — Previous 
Owen,  1847-50 
Whittlesey,  1860 
Irving,  1873-78 
Sweet,  1873-77 
Irving,  1881  . 
Winchell,  1872-99 
Grant,  1899-1900 
Collie,  1900  . 
Hall,  1901-08 
Lane,  1908  . 
Grout,  1910  . 
Bibliography 


Chapter  III — The  Bayfield 
Limits  of  the  Group 
Areal  Extent 
Subdivisions 


Investigations 


Sandstone  Group 


6 
6 
7 
7 
8 
8 
9 
11 
12 
12 

14 
14 
15 
15 
16 
16 
17 
19 
20 
20 
21 
21 
21 

25 
25 
25 
2(5 


iv 


CONTENTS 


CHAPTER  III,  continued: 
Composition  . 
Shale  Beds  . 
Bedding- 
Iron  Banding 
Pebbles  and  Clay  Pockets 
Chequamegon  Sandstone 

General  Character  and  Extent 
Thickness  . 
General  Section 
Local  Details 
Devil's  Island  Sandstone 

General  Character  and  Extent 
Thickness  . 
Rippie  Marks 
Cross-bedding 
Orienta  Sandstone  . 

General  Character  and  Extent 
Thickness 
General  Section 
Local  Details  . 
Economic  Products 
Condition  of  the  Quarry  Business  in  1910 
Causes  of  Decline  . 


Chapter  IV- — Oronto    Group  and    Older   Formations,  and 


the  Extension  of  the  Sandston 
Minnesota 
Nomenclature 
General  Character  . 
Areal  Extent 
Thickness  . 
Subdivisions 
Composition 
Bedding 
Local  Details 

Amnicon  Formation 

Eileen  Sandstone 

Freda  Sandstone 

Nonesuch  Formation 

Outer  Conglomerate 
Older  Formations  . 

The  Traps 

The  Pre-Keweenawan  Rocks 
Economic  Products 
The  Extension  of  the  Sandstone  Groups  into  Minnesota 


Page 
26 
28 
29 
31 
32 
33 
33 
33 
33 
34 
38 
38 
39 
39 
40 
41 
41 
41 
41 
42 
45 
46 
46 


e    Groups  in 


CONTENTS 


V 


Chapter  V  The  Relation  op  the  Bayfield  and  Oronto  Sand 

stone  Groups 
General  Statement 
Fish  Creek 
Ashland  Well 
Middle  River 
St.  Louis  River 
Summary 

•Chapter  VI— The  Contact  of  the  Bayfield  Group  with  the 


Traps  .  .  .         ..  .  .  75 

General  Statement  .......  75 

Douglas  Fault        .......  75 

Local  Details    .  .  .  .  .  75 

Middle  River  Contact       .....  76 

Amnicon  River  Contact    .  .  .  .  .77 

Copper  Creek        ......  80 

Falls  of  Black  River        .  .  .   .  .80 

Interpretation  of  Exposures         .  .  .  .  .81 

North  Coast  Contact  -    .  .  .  .  .84 

St.  Louis  River  Contact      ......  84 

Contact  with  the  Slates      ......  87 

Chapter  VII— The  Structure  of  the  Wisconsin  Coast  of  Lake 

Superior       ......  88 

General  Statement  .......  88 

Douglas  Fault         .......  89 

North  Coast  Fault  .  .  .  .  .  .  91  . 

St.  Louis  River       .......  91 

Folds  near  Ashland  ......  92 

Structure  of  the  Bayfield  Group    .  .  .  .  .94 

Age  of  the  Deformation      .  .  .  .  .  .95 

Origin  of  West  End  of  Lake  Superior       .  .  .  .95 

Table  showing  Direction  of  Joints  and  Faults — West  End  of 

Lake  Superior  .......  96 

Chapter  VIII — Conclusions  ......  100 

General  Statement  .......  100 

Summary  of  Lithologic  Characters  ....  100 

Comparisons  with  Sandstones  of  Southern  Wisconsin     .  .  101 

Origin  of  the  Sandstones    ......  101 

Age  of  the  Bayfield  Group  .  .  .  .  .102 

Summary  of  Geological  History     .....  105 

Oronto  Group    .......  106 

Bayfield  Group  ......  107 

Summary  of  Conclusions    ......  108 

Index     .........  110 


ILLUSTRATIONS. 


PLATES 

Page 

I    A,  Beach  of  Lake  Superior;  B,  Bedding  on  Outer  Island 

•  .  .  Frontispiece 

II    Birdseye  view  of  west  end  of  Lake  Superior  .  .  8 

III  Photomicrographs  of  Chequamegon  Sandstone:  A,  Houghton; 

B,  Basswood  Island  .  .  .  .  .26 

IV  A,  Bedding  on  Sand  Island;  B,  Bedding  near  Herbster       .  30 
V    A,  Sea  Caves,  Sand  Island;  B,  Sea  Caves,  Squaw  Bay        .  40 

VI  Photomicrographs  of  Orienta  Sandstone:  A,  Port  Wing;  B, 

St.  Louis  River        .  .  .  .  .  .44 

VII  Amnicon  Formation,  Middle  River    .  .  .  .50 
VIII    Eileen  Formation,  Fish  Creek          _          .  .  .52 

IX    Map  of  Clinton  Point  exposures        .  .  .  .54 

X    Photomicrographs:  A,  Clinton  Point;  B,  Fish  Creek  .  56 

XI    A,  Freda  Sandstone,  Oronto  River;  B,  Falls  of  White  River  58 
XIa  Map  of  Fish  Creek  exposures  .  .  .  .62 

Xlb  Views  on  Fish  Creek    .  .  .  .  .  .64 

XIc  Views  on  Fish  Creek    .  .  .  .  .  .64 

XII  Photomicrographs,  Fish  Creek  .  .  .  " .  66 

XIII  Map  of  Middle  River  exposures         .  .  .  .66 

XIV  Photomicrographs,  Middle  River       .  .  .  .68 

XV  Map  of  St.  Louis  River  exposures       .  .  .  .70 

XVI  Photomicrographs:  A,  Middle  River;  B,  St.  Louis  River     .  72 

XVII  A,  View  on  St  Louis  River;  B,  Middle  River  contact        .  74 

XVIII  Amnicon  River  Contact,  east  bank  .  .  .  .76 
XVIIIa  A,  Lower  Falls,  Amnicon  River;  B,  Contact,  west  bank    .  78 

XIX    Map  of  Falls  of  Black  River  .  .  .  .80 

XX    Sections  on  St.  Louis  River    .  .  .  .  .86 

XXI    Views  on  Middle  River  .  .  .  .90 

XXII    Views  on  Amnicon  River       .  .  .  .  .92 

XXIII    A,  Sea  Caves,  Squaw  Bay;  B,  Fault  on  St.  Louis  River     .  94 

FIGURES  IN  TEXT 

Fig.  1  Bedding  in  Orienta  sandstone,  Siskowit  Pt.,  Bayfield  County  29 
Fig.    2    Channel  in  Sandstone  Layers-^Quarry  northeast  of  Wash 

burn,  Bayfield  County        .  .  .  .  .29 


viii 


ILLUSTRATIONS 


Fig.    3    Bedding  in  Orienta   sandstone,    Amnicon   River,  Douglas 

County  .  .  .  .  .  .  .30 

Fig.    4    Types  of  Ripple  Marks  .  .  .  .  .  .40 

Fig.    5    Ripple  Marks  in  Devils  Island  Sandstone       .  .  .40 

Fig.    6    Magnetite  sand  bed  in  Eileen  sandstone,  Fish  Creek,  Bayfield 

County  .  .  .  .  .  .  .53 

Fig.    7    Bedding  in  Eileen  sandstone,  Fish  Creek,  Bayfield  County  .  55 
Fig.    8    Diagram  showing  use  of  cross-bedding,  in  determining  top 

of  vertical  strata       .  .  .  .  .  .63 

Fig.    9    Bedding  in  Amnicon  formation,  St.  Louis  River,  Minnesota  69 
Fig.  10   Sketch  map  showing  contact  of  trap  and  sandstone  on  Amni- 
con River,  Douglas  County  .  .  .  .  .77 

MAP 

West  End  of  Lake  Superior.  .         .         .         .in  pocket 


INTKODUCTION 


Purpose  of  the  Investigation.  The  study  made  by  the 
writer  in  1910,  the  conclusions  of  which  are  set  forth  in  this 
report,  was  to  determine,  so  far  as  possible,  the  age,  origin,  and 
N  stratigraphic  relations  of  the  red  sandstones  of  the  Wisconsin 
coast  of  Lake  Superior.  These  rocks  are,  so  far  as  known,  en- 
tirely devoid  of  organic  remains.  They  were  at  an  early  day 
divided  into  two  great  groups.  Of  these  the  older  is  character- 
istically composed  of  grains  which  are  mainly  feldspars  and 
fragments  of  igneous  rocks,  and  the  strata  are  nearly  always 
considerably  tilted.  On  the' other  hand,  the  upper  and  younger 
group  is  almost  wholly  quartz  sandstone,  and  its  beds  are  in 
general  approximately  horizontal. 

Former  investigators  recognized  that  the  lower  group  was  a 
part  of  the  Keweenawan  series,  but  opinions  differed  as  to  its 
relation  to  the  upper;  some  held  that  they  were  conformable, 
while  others  maintained  that  an  unconformity  existed,  and 
that  the  upper  group  probably  corresponded  to  the  Cambrian 
of  southern  Wisconsin,  or  its  conformable  downward  extension. 

Summary  of  Results.  One  of  the  main  results  of  the  pres- 
ent study  was  the  discovery  of  the  fact  that  th'ere  is  a  conform- 
able downward  gradation  from  the  upper  quartz  sandstone  sed- 
iments into  red  shales  and  arkose  sandstones  which  possess  the 
same  characters  as  the  main  body  of  the  recognized  Upper  Ke- 
weenawan sediments.  At  one  locality  it  was  found  that  highly 
tilted  feldspathic  sediments  almost  unquestionably  belonging  to 
the  Keweenawan  series  grade  conformably  upward  into  quartz- 
ose  beds,  lithologically  indistinguishable  from  and  probably  con- 
tinuous with  the  upper  group.  Furthermore,  no  evidence  was 
discovered  which  tended  to  indicate  that  the  two  groups  are  un- 
conformable. While  the  evidence  is  not  positively  conclusive, 
owing  to  the  scarcity  of  outcrops,  it  is  believed  that  tire  facts 


2 


INTRODUCTION. 


warrant  the  conclusion  that  the  sandstones  form  a  single  con- 
formable series,  so  that  what  has  heretofore  been  called  the 
''Western  sandstone"  (here  called  the  Bayfield  group)  is  con- 
formable with  the  underlying  Upper  Keweenawan  arkose  sedi- 
ments (here  called  the  Oronto  group).  The  results  of  this  work 
show  that  the  contact  of  the  upper,  or  Bayfield,  group  with  the 
Middle  Keweenawan  traps  is  a  fault.  There  is  some  evidence  of 
unconformity  at  this  contact.  However,  it  is  shown  that  if 
faulting  took  place  prior  to  or  during  the  deposition  of  the 
sandstone,  the  resulting  local  unconformity  along  the  fault  scarp 
would  not  demonstrate  a  great  lapse  of  time  between  the  deposi- 
tion of  the  adjacent  strata,  Indeed,  it  seems  certain  that  fold-, 
ing,  faulting,  and  erosion  went  on  during  the  deposition  of 
the  entire  sandstone  series,  and  that  the  upper  beds  therefore 
overlapped  with  slight  unconformity  upon  the  older  strata  of 
the  same  series.  The  difference  in  degree  of  folding  of  the  two 
groups  of  sandstone  is  correlated  with'  this  fact  and  with  the 
general  structure  of  the  region.  Although  no  decisive  opinion 
can  at  present  be  reached,  it  appears  probable  that  both  groups 
were  deposited  upon  the  land  in  a  basin  formed  by  the  folding 
of  the  earlier  Keweenawan  rocks. 

A  detailed  study  of  the  lower  sandstone  group  was  not  under- 
taken. 

It  seems  probable  that  the  so-called  "red  clastic  series"  which 
fills  the  continuation  of  the  Lake  Superior  synclinal  beneath  the 
flat-lying  Paleozoic  rocks  of  Minnesota,  is  the  continuation  of 
the  red  sandstone  of  the  Lake  Superior  coast.  But,  as  no  con- 
tact between  these  rocks  and  the  recognized  light-colored  marine 
Upper  Cambrian  strata  is  known  to  be  exposed,  no  definite 
opinion  as  to  their  relations  can  be  formed.  The  results  of  this 
study,  therefore,  do  not  in  any  way  affect  the  question  of  the 
age  of  the  Keweenawan  with  reference  to  the  Cambrian  of  the 
Mississippi  valley.  The  evidence  necessary  to  determine  this 
question  must  be  sought  for  along  the  extension  of  the  upper 
sandstone  group  (Bayfield  group)  into  Minnesota.  However, 
the  fact  that  the  Bayfield  group  was  involved  in  the  profound 
deformations  of  the  Keweenawan  period,  contrasts  it  sharply 
with  the  slightly  disturbed  strata  of  the  recognized  Cambrian 
of  .  Wisconsin  and  Minnesota.    It  therefore  appears  from  the 


INTRODUCTION. 


3 


evidence  at  hand  that  the  Bayfield  group  is  more  closely  allied 
to  the  Algonkian  than  to  the  Cambrian. 

The  question  of  the  equivalency  of  the  Bayfield  group  to  the 
supposed  Cambrian  sandstones  of  the  east  side  of  Keweenaw 
Point  is  not  considered  in  this  report.  Both  formations  are 
barren  of  fossils  and  are  separated  by  a  wide  area  of  older  rocks, 
so  that  no  correlation  can  be  attempted  with  the  evidence  now 
at  hand. 

Method  of  Field  Work.  The  region  in  which  the  forma- 
tions under  investigation  are  situated  is  very  sparsely  settled, 
and  hence  only  accesible  with  considerable  difficulty.  A  light 
launch  was  designed  especially  for  the  Survey  by  Dr.  Kent  T. 
Wood  of  Madison.  This  novel  craft  weighed  about  250  pounds 
when  ready  to  run,  but  could  carry  three  times  that  weight. 
An  efficient  and  reliable  gasoline  engine  gave  it  a  speed  of 
over  seven  miles  an  hour  on  a  fuel  consumption  of  one  gallon 
for  twenty  miles.  The  launch  was  very  seaworthy,  even  more 
so  than  many  larger  craft,  and  possessed  the  great  advantage 
of  light  weight,  permitting  it  to  be  drawn  up  on  the  beach  out 
of  the  way  of  the  sudden  and  violent  storms.  (See  frontispiece, 
Plate  I,  A).  Little  time  was  lost  on  account  of  high  winds;  and 
the  engine  never  failed  to  start,  even  when  the  boat  was  nearly 
swamped  while  being  launched  into  the  breakers.  A  further 
advantage  was,  that  the  light  draught  permitted  running  close  to 
the  shore.  All  of  the  coast  exposures  were  examined  in  this 
manner,  landings  being  made  on  the  rocks  whenever  anything 
of  interest  was  observed.  About  a  thousand  miles  were  travelled 
on  the  lake  and  its  tributary  streams  in  the  three  months  de- 
voted to  field  work. 

Maps.  On  shore,  the  geologist  working  on  a  rapid  survey 
is  obliged  to  contend  with  the  fact  that  there  are  no  accurate 
maps  of  the  region.  The  township  plats  of  the  Land  Survey, 
while  much  better  than  nothing,  are  quite  inaccurate,  especially 
in  Iron  County.  Section  corners,  except  a  few  recently  marked, 
can  only  be  found  with  trouble  and  delay,  and  few  roads  or 
fences  follow  the  land  division  lines.  It  is  difficult  to  keep  one's 
location  at  all  accurately  when  following  the  rocky  bed  of  a 
winding  stream.  All  rivers  and  creeks  on  which  any  exposures 
were  reported  by  former  geologists  or  by  present  inhabitants  of 


INTRODUCTION. 


the  district,  were  examined  as  thoroughly  as  the  limited  time 
available  would  permit  and  the  importance  of  tht  formation 
seemed  to  warrant. 

The  base  for  the  geological  map  is  the  general  chart  of  the 
west  end  of  Lake  Superior,  prepared  by  the  U.  S.  Lake  Survey.1 

This  is  accurate  only  so  far  as  the  navigation  of  large  vessels 
requires.  In  shallow  water  and  on  shore  it  is  unreliable.  The 
township  lines  were  adjusted  to  this  base,  the  inland  part  of  the 
map  being  based  chiefly  upon  the  plats  of  the  IT.  S.  Land  Sur- 
vey. The  roads  are  corrected  from  observations  by  F.  L.  Mus- 
back  of  the  Soils  Division  of  the  Geological  and  Natural  History 
Survey  and  the  writer,  rs  well  as  from  plats  furnished  by  town 
c^rks  and  others. 

Acknowledgments.  Tbo  writer  Avas  assisted  by  E.  Tl. 
Toole  of  Baraboo.  Wisconsin,  then  a  student  in  the  University 
of  Wisconsin,  who  also  spent  some  of  his  time  in  collecting  plants 
and  water  life.  For  the  last  three  weeks  of  the  season,  Thomas 
Turvill  of  Madison  gratuitously  contributed  his  services. 

Tbe  work  was  carried  on  under  the  direction  of  W.  0.  Hotch- 
kiss,  State  Geologist,  and  E.  A.  Birge,  Director  of  the  Wiscon- 
sin Geological  and  Natural  History  Survey.  Much  valuable 
information  was  obtained  from  F.  L.  Musback  of  the  Soils  Div- 
ision of  this  Survey,  who  covered  all  the  area  east  of  Eange  12 
W.  In  the  preparation  of  the  report,  most  of  those  who  have 
been  interested  in  the  question  were  consulted.  The  waiter 
wishes  to  express  his  indebtedness  to  Prof.  U.  S.  Grant  of  North- 
western University,  Prof.  F.  F.  Grout  of  the  University  of  Min- 
nesota, Prof.  A.  C.  Lane,  formerly  State  Geologist  of  Michigan, 
Prof.  C.  K.  Leith  of  the  University  of  Wisconsin,  and  Dr.  Sam- 
uel Weidman  of  this  Survey. 

Acknowledgments  are  also  due  to  Hon.  S.  S.  Fifield,  post- 
master of  Ashland,  and  his  assistants,  for  much  valuable  aid  at 
the  beginning  of  the  expedition ;  to  Prof.  J.  A.  Merrill  of  the 
Superior  State  Normal  School  for  well-records  and  other  help ; 
to  A.  E.  Appleyard,  president  of  the  Ashland  Light,  Power  & 
Street  Kailway  Co. ;  to  J.  E.  Johnson,  Jr.,  manager  of  the  Lake 
Superior  Iron  and  Chemical  Co. ;  to  F.  N.  Lang  of  Bayfield  and 


i  U.  S.  Lake  Survey  Office,  Detroit,  Mich.,  Chart  96. 


INTRODUCTION. 


5 


C.  N.  Edin  of  Dedham — the  last  three  having  furnished  well- 
records;  to  the  officers  and  men  of  the  John  Schroeder  and  J.  S. 
Stearns  lumber  companies,  and  the  Good  Land  Company  of 
Ashland,  for  information  and  assistance;  to  William  Foley  of 
Ashland,  to  whose  infomation  is  due  the  discovery  of  the  im- 
portant outcrops  on  Fish  Creek;  and  to  many  others,  too  num- 
erous to  mention,  who  treated  our  party  with  great  kindness 
and  hospitality. 

Expedition  of  1912.  In  June,  1912,  the  writer  spent  a  week 
in  re-examining  several  important  localities,  A  detailed  plane 
table  map  was  made  of  the  important  exposures  on  the  South 
Fork  of  Fish  Creek,  near  Ashland,  and  a  careful  but  unsuccess- 
ful search  was  made  for  exposures  between  these  and  the  known 
area  of  the  Bayfield  group  to  the  north.  References  to  the  re- 
sults of  this  expedition  have  been  incorporated  in  the  text.  No 
observations  were  made  which  materially  changed  any  of  the 
opinions  formed  as  a  result  of  the  earlier  survey. 


6 


TOPOGRAPHY. 


CHAPTER  I 


THE  TOPOGRAPHY  OF  THE  WISCONSIN 
COAST  OF  LAKE  SUPERIOR. 


General  Statement.  In  order  to  arrive  at  a  better  under- 
standing of  the  geology  of  the  Wisconsin  coast  of  Lake  Superior, 
a  brief  review  of  the  main  topographic  features  of  the  district 
is  desirable.1  This  region  may  be  divided  into  the  following 
more  or  less  well-defined  districts : 

The  Southern  Highland,  including  the  Penokee  Range,  the 
plateau  south  of  it,  and  the  trap  hills  immediately  to  the 
north. 

The  Trap  Ranges  of  Douglas  County  and  the  north  coast. 
The  Bayfield  Ridge,  including  the  Pine  Barrens  to  the 

southwest. 
The  Apostle  Islands. 


i  More  detailed  accounts  of  the  topography  and  physiography  will  be 
found  as  follows: 

Irving,  R.  D.,  Geology  of  Wisconsin,  1873-9,  vol.  Ill,  pp.  60-211. 
Sweet,  E.  T.,  Ibid,  pp.  310-352. 

Krey,  J.,  Lake  Superior  and  Mississippi  Canal,  House  Doc.  330, 
54th  Congress,  1st  Session,  1896. 

Collie,  G.  L.,  Wisconsin  Shore  of  Lake  Superior,  Bulletin  Geologi- 
cal Society  of  America,  vol.  XII,  1901,  p.  199. 

Case,  E.  C,  Wisconsin,  Its  Geology  and  Physical  Geography,  Mil- 
waukee, 1907. 

Martin,  L.,  Geology  of  Lake  Superior  Region,  Monographs  U.  S. 
Geological  Survey,  vol.  LIL  1911,  pp.  85-117. 


TOPOGRAPHY. 


7 


The  Western  Plain. 
The  Eastern  Plain. 

The  Southern  Highland.  The  highest  elevations  occur  at 
the  southeastern  corner  of  the  area  shown  on  the  accompany- 
ing map  and  birds-eye  view  (Plate  II,  p.  8)  ;  but  as  seen  from 
the  lake  this  region  because  of  its  distance  is  not  as  impressive  as 
some  of  the  other  features.  The  level  skyline  seen  from  the  lake 
is  formed  by  the  southernmost  ridge,  sometimes  known  as  the 
Grabbro  Range,  of  Keweenawan  traps,  whose  northward-dipping, 
steeply-inclined  beds  underlie  the  north  slope  of  this  highland. 
At  its  base  is  found  a  low  escarpment,  formerly  known  as  the 
Copper  Range,  which  marks  the  border  of  the  traps  where  they 
are  overlain  by  the  sandstones  of  the  lowlands  to  the  north.  The 
lower  slopes  are  often  heavily  mantled  with  glacial  drift,  but  at 
higher  levels  there  appear  bare  ridges  or  hogbacks  of  rock. 
These  culminate  in  the  great  escarpment,  or  Gabbro  Range,  which 
overlooks  the  longitudinal  valley  to  the  south,  followed  by  the 
railway.  This  valley  is  underlain  by  slates,  graywacke,  and 
iron  formation  of  Huronian  age. 

Beyond  this,  farther  still  to  the  south,  rises  the  Penokee 
Range  of  slate,  quartzite,  and  lean  iron  formation,  the  summits 
of  which  are  some  1,200  feet  above  the  lake  or  1,800  feet  above 
tide,  exceeding  but  little  the  elevation  of  the  trap  ridge  to  the 
north.  An  abrupt  slope  on  the  south  side  of  the  Penokee  Range 
leads  down  a  hundred  feet  or  more  to  the  rolling  upland  under- 
lain by  Archean  granites  and  metamorphic  rocks.  The  streams 
having  their  sources  in  this  area  cross  the  ridges  through  deep 
gaps.  The  larger  ones  seldom  follow  the  strike  of  the  rocks  for  any 
great  distance,  though  the  strike  determines  the  major  lineaments 
of  tire  country.  The  tumultuous  descent  of  the  streams  usually 
ends  in  a  high  fall,  where  the  soft  sandstone  is  reached.  Nearly 
all  of  these  streams  exhibit  magnificent  rock  exposures,  and 
outcrops  are  abundant  throughout  the  Southern  Highland  dis- 
trict, only  a  portion  of  them  being  shown  on  the  map. 

The  Trap  Ranges:  Douglas  County.  Stretching  across 
Douglas  County  in  the  western  part  of  the  district,  is  a  compara- 
tively low  and  much  broken  ridge,  or  rather  a  series  of  ridges, 
known  as  the  " Douglas  Range,"  "Copper  Range,"  or  "South 
Range."    Its  summits  do  not  extend  much*  over  500  feet  above 


8 


TOPOGRAPHY. 


the  lake,  so  that  as  seen  from  the  coast  it  is  not  very  striking. 
The  southern  slopes  are  rather  gentle,  but  on  the  north  is  a 
descent  of  50  to  300  feet  to  the  plains  which  border  the  lake. 
This  ridge  is  underlain  by  Keweenawan  traps,  moderately  in- 
clined to  the  southeast,  and  the  escarpment  marks  the  contact 
with  the  sandstones  to  the  north.  The  streams  cross  through 
gaps  and  descend  in  falls  to  the  lowlands. 

North  Range.  Along  the  north  coast  in  Minnesota  occurs 
another  range  of  similar  rocks,  also  dipping  to  the  southeast.  It 
is  higher  than  the  South  Range,  and  the  serrated  summits  which 
are  visible  from  the  south  coast  on  any  clear  day,  form  a  very 
striking  skyline.  A  few  miles  southwest  of  Duluth  this  range 
ends  in  a  bold  bluff  about  450  feet  in  height.  (See  Duluth  sheet, 
U.  S.  Geol.  Survey,  and  Duluth  plate,  Geology  of  Minnesota,  vol. 
IV,  p.  566.) 

The  Bayfield  Ridge.  The  broad  peninsula  which  stretches 
out  into  the  lake  east  of  the  Douglas  Range,  off  the  end  of  which 
lie  the  Apostle  Islands,  is  for  the  greater  part  of  its  length  the 
most  conspicious  topographic  feature  of  the  district.  The  aver- 
age elevation  of  its  summit  is  nearly  700  feet  above  the  lake,  or 
1,300  feet  above  the  sea.  Topographically,  it  is  a  continuation  of 
the  Douglas  Range  and  the  high  country  to  the  south  of  it,  but 
unlike  the  elevations  previously  described,  the  Bayfield  Ridge 
so  far  as  known  consists  wholly  of  drift.  Except  along  the 
shore  and  a  few  of  the  deepest  valleys,  exposures  of  solid  rock 
are  absolutely  wanting;  and  these  are  all  of  sandstone  instead 
of  igneous  rocks. 

The  borders  and  the  northeastern  extremity  of  this  ridge  are 
cut  up  into  ridges  and  isolated  hills  which  have  the  appearance 
of  land  forms  due  to  erosion.  Up  to  a  level  of  500  to  550  feet 
above  the  lake  are  found  terraces  cut  by  the  waves  of  former 
lakes  held  at  these  levels  by  the  slowly  retreating  glaciers.  These 
abandoned  beaches  run  around  the  isolated  hills  and  along  the 
ridges,  often  producing  the  impression  of  rock  escarpments.  The 
slopes  are  cut  by  many  deep  ravines. 

The  summit  of  the  Bayfield  Ridge  shows  considerable  areas  of 
very  rough,  sandy,  glacial  moraine;  the  pits  between  the  hum- 
mocks are  among  the  largest  in  the  state,  being  often  over  150 
feet  in  depth,  and  separated  from  one  another  by  extremely  nar- 


TOPOGRAPHY. 


9 


row  sharp  ridges.  Towards  the  southwest,  this  sandy  country, 
called  the  "Pine  Barrens/'  is  of  less  relief.  A  striking  feature 
of  this  entire  upland  is  the  absence  of  streams;  lakes  are  found, 
however,  the  water  being  prevented  from  seeping  away  by  the 
occurrence  of  a  clay  layer  at  a  moderate  depth.  The  Barrens 
present  a  most  desolate  appearance,  now  that  all  the  timber  has 
been  cut.  Only  a  few  burnt  stubs  are  left  standing  out  mourn- 
fully above  the  sweet  fern,  scrub  oaks,  and  low  second  growth. 

The  Apostle  Islands.  If  we  follow  the  Bayfield  Ridge  to  the 
northeast,  where  it  is  broken  up  into  separate  hills,  we  will  find 
that  the  same  sort  of  topography  extends  beneath  the  surface  of 
the  lake,  the  summits  of  the  hills  forming  the  famous  Apostle 
Islands.  These  islands  were  so  named  because  once  they  were 
erroneously  supposed  to  be  twelve  in  number.  Twenty-two 
islands  now  exist,  one  having  succumbed  to  the  attacks  of  the 
waves,  and  another  having  been  cut  in  two  since  the  coming  of 
the  first  explorers.  A  study  of  the  contours  of  the  lake  bottom 
(see  m'ap)  and  bird's  eye  view  (Plate  II,  p.  8)  shows  the  rela- 
tion of  the  group  to  the  topography  of  the  mainland.  There  are 
a  number  of  shoals  which  a  slight  fall  of  the  water  level  would 
make  into  islands,  and  the  same  water  stage  would  join  some  of 
the  present  islands  to  the  mainland.  On  the  other  hand,  the  rise 
of  the  waters  would  submerge  several  islands  and  surround  some 
of  the  hills  near  the  coast.  "With  the  gradual  lowering  of  the 
lake  level  since  glacial  times,  there  has  been  a  progressive  change 
in  the  composition  of  the  Apostle  group.  The  mainland  has 
steadily  been  extended  to  the  northeast,  while  lower  and  lower 
shoals  have  in  turn  become  islands. 

The  present  islands  range  in  size  from  Madeline,  twelve  and 
one-half  miles  in  length,  to  mere  rocks,  like  Little  Manitou.  They 
vary  from  a  height  which  is  barely  above  the  storm  waves,  to  an 
elevation  of  480  feet  on  Oak  Island.  Outer,  Stockton,  and  Bear 
Islands  are  the  only  others  to  exceed  100  feet  in  altitude,  most 
being  flat  and  low.  The  higher  ones  are  terraced  by  abandoned 
beaches,  none  of  which,  so  far  as  known,  exposes  any  rock. 

The  waves  of  the  present  level  have  cut  deeper  into  the  land 
than  at  any  other  stage,  with  the  possible  exception  of  the  highest 
(see  p.  13).  Their  work  may  be  seen  in  the  cliffs,  bars,  and 
beaches. 


10 


TOPOGRAPHY. 


The  cutting  due  to  the  present  stage  of  the  lake  has  exposed 
cliffs  of  the  red  sandstone.  They  do  not  exceed  60  feet  in 
height,  and  are  almost  always  capped  with  broken  rock  and 
drift.  All  are  lined  at  the  foot  with  fallen  blocks,  which,  how- 
ever, break  up  rapidly,  so  that  there  is  little  sandstone  shingle. 
These  fallen  fragments,  submerged  ledges  which  sometimes  form 
dangerous  reefs,  and  the  clean,  reddish,  sharp  sands  derived 
from  their  breaking  up,  may  all  be  seen  through  the  clear,  cold, 
greenish  waters  of  the  lake.  In  thin-bedded  layers  only,  have 
the  waves  worn  any  striking  sea  caves.  The  best  are  on  Devils 
Island  and  near  Squaw  Bay  to  the  southwest ;  but  small  ones, 
as  well  as  deep  coves  along  joint  planes,  are  seen  on  the  eastern 
end  of  Stockton  Island  and  at  a  few  other  points  (see  Plates  I, 
B,  frontispiece;  IV,  p.  30;  V,  p.  40;  XXIII  A,  p.  94). 

A  large  portion  of  the  shore  line  is  drift.  The  materials  ex- 
posed in  the  cliffs  are  mainly  stony  red  clay,  although  the 
tendency  of  this  material  to  slump  down  the  bank  gives  one  an 
undue  idea  of  its  abundance.  Sandy  till,  gravel,  and  clean 
white  or  reddish  sands  are  probably  more  abundant.  So  far  as 
the  writer's  observations  go,  they  underlie  the  red  clay  or  clay 
till.  Sand  beaches  are  very  common  but  are  usually  thickly 
strewn  with  boulders  washed  out  of  the  drift.  Huge  fields  of 
these,  thickly  paving  the  bottom,  are  frequently  seen.  Much  of 
the  ground  marked  as  " rocky"  on  the  chart  is  of  this  character. 
Spits  of  clear  sand  are  found  on  the  sides  of  the  islands  toward 
the  mainland,  that  is,  on  the  most  sheltered  side.  These  spits 
have  usually  been  built  out  from  both  sides  and  often  enclose  a 
pond  or  swamp.  At  the  outer  ends  is  usually  a  rapid  descent 
into  deep  water.  Some  seem  to  be  now  wasting  away,  as  on 
Madeline  Island,  in  which  case  they  extend  lakeward  as  shoals. 
Many  bays  have  been  cut  off  by  beaches  and  in  some  cases  the 
action  of  the  waves  has  joined  two  rocky  islands  into  one.1 

The  islands  are  nearly  all  densely  wooded,  some  magnificent 
forest  being  seen  in  places.  Hemlock,  balsam,  birch,  and  maple 
predominate.   The  dark  foliage,  together  with  the  prevailing  red 

i  The  bar  connecting  Sand  Island  and  the  mainland  does  not  appear 
to  be  wholly  wave  work.  Cf.  Collie,  G.  L.,  Wisconsin  Shore  of  Lake 
Superior,  Bull.  Geol.  Soc.  Amer.,  vol.  12,  1901,  p.  199. 


TOPOGRAPHY. 


11 


color  of  the  drift  and  rocky  shores,  give  the  islands  a  rather 
somber  and  forbidding  appearance. 

Permanent  settlement  is  confined  to  Sand  and  Madeline  Is- 
lands, but  light-houses  and  fishing  stations  are  found  on  most  of 
the  group.  Now  that  the  quarries  are  abandoned,  sand  is  the 
only  geological  product  (see  p.  27).  Several  dredges  take  this 
material  to  Duluth  from  the  spit  on  Oak  Island. 

The  Western  Plain.  West  from  the  little  settlement  at 
Herbster  on  the  northwest  side  of  the  Bayfield  peninsula,  the 
main  body  of  the  great  Bayfield  Ridge  leaves  the  coast.  To  the 
southwest  stretches  a  broad  sloping  plain,  broken  at  first  by  a 
few  isolated  hills  like  those  near  the  end  of  the  headland.  For 
the  most  part  of  its  length  it  is  bounded  on  the  southeast  by  the 
escarpment  of  the  Douglas  or  South  Range ;  but  in  some  places 
where  this  is  ill  defined,  it  extends  across  the  line  of  the  traps 
up  to  the  highest  abandoned  shore  line  which  is  found  to  the 
south  upon  the  Pine  Barrens.  Near  Superior  the  plain  broadens, 
being  bounded  on  the  north  by  the  North  or  Minnesota  Range. 
.  The  surface  of  the  plain  is  not  level  but  slopes  toward  the 
lake  at  the  rate  of  nearly  fifty  feet  per  mile;  the  inclination 
southwest  of  Superior,  measured  along  the  line  of  the  axis  of  the 
lake  basin,  is  much  less. 

No  prominent  beach  terraces  can  be  seen  on  the  surface  of 
this  plain,  which  is  broken  only  by  slight  marshy  sags.  It 
is  dissected  by  narrow,  steep-sided  valleys  cut  by  the  numerous 
streams  in  the  underlying  soft  red  clay  and  fine  sand.  These 
valleys  range  from  a  few  feet  to  over  100  feet  in  depth,  with  a 
flat  bottom  sometimes  more  than  a  quarter  of  a  mile  in  width. 
The  abundance  of  streams  contrasts  sharply  with  their  rarity  in 
the  regions  of  porous  sandy  subsoil. 

The  lake  shore  (Plate  I,  A,  frontispiece)  is  a  steep  cliff  except 
at  the  mouths  of  rivers,  where  clean  sand  beaches  occur.  At  the 
foot  of  this  cliff  is  usually  a  stony  beach.  In  the  valleys  of  the 
streams  and  in  the  shore  cliff  are  found  infrequent  exposures 
of  the  red  sandstone  underlying  the  drift. 

At  the  head  of  the  lake,  southwest  from  Superior,  is  a  very 
irregular  shore  line  caused  by  the  drowning  of  the  valleys  by 
the  waters  of  the  lake  (see  p.  13).    Two  long  sandy  beach  ridges 


12 


TOPOGRAPHY. 


known  as  Minnesota  and  Wisconsin  points,  cross  the  end  of  the 
lake,  enclosing  Superior  and  St.  Louis  bays. 

The  Eastern  Plain.  In  northern  Ashland  County,  between 
the  Southern  Highland  and  the  Bayfield  Ridge,  is  a  plain  which 
differs  only  from  the  Western  Plain  in  being  more  thickly  dotted 
with  sandy  ridges  and  hills.  The  slope  of  this  plain  is  about  ten 
feet  per  mile  in  the  middle,  but  it  is  steeper  where  it  laps  up 
against  the  highlands  to  the  south.  To  the  northwest  it  merges 
into  the  Bayfield  Ridge,  spurs  of  which  extend  out  between  the 
streams.  The  surface  of  the  plain  is  cut  by  steep-sided  valleys, 
some  of  which  are  over  a  half  mile  in  width. 

Between  the  irregular  shore  line  of  the  Bayfield  peninsula  and 
the  Apostle  Islands,  and  the  point  where  the  Southern  High- 
land strikes  the  lake  at  Clinton  Point  in  Iron  County,  stretches 
a  smooth  sweep  of  sand  beach.  Its  western  extremity,  known  as 
Chequamegon  Point  and  Long  Island,  separates  a  great  depres- 
sion in  the  shore  line  from  the  open  lake  ;  this  is  Chequamegon 
Bay.  For  the  most  part  this  bay  is  very  shallow,  especially  on 
the  east  side  where  the  bottom  is  a  continuation  of  the  low 
marshy  country  behind  the  beach  ridge  north  of  Odanah.  The 
small  break  between  the  point  and  the  island  is  called  the  Sand 
Cut  and  is  said  to  have  been  first  formed  by  a  great  storm  in 
1872. 1  As  this  low  ridge  alone  protects  the  large  bay  from  the 
violent  northeast  winds,  it  does  not  form  a  good  harbor.  A 
breakwater  has  been  found  necessary  at  Ashland. 

Outline  of  Surficial  Geology.  The  subject  of  the  Pleisto- 
cene geology  of  this  district  is  at  present  under  investigation  by 
Mr.  Frank  Leverett  of  the  U.  S.  Geological  Survey,  and  the  Soils 
Division  of  this  Survey  is  engaged  in  a  study  of  the  soils  and 
agricultural  conditions.  The  U.  S.  Bureau  of  Soils  has  pub- 
lished two  reports  upon  the  part  of  the  area  west  from  Range  12 
West.2  Although  little  time  was  given  by  the  writer  to  the 
subject  of  the  surface  geology,  a  brief  summary  of  its  main 
points  will  be  given. 

1  Irving,  R.  D.,  Geology  of  Wisconsin,  1873-9,  vol.  TIT,  p.  71.  Collie, 
G.  L.,  Wisconsin  Shore  of  Lake  Superior,  Bull.  Geol.  Soc.  Amer.,  vol.  12, 
1901,  p.  199. 

2  U.  S.  Dept.  of  Agriculture,  Soil  Surveys  of  the  Carlton  and  Su- 
perior Areas,  Field  Operations,  Bureau  of  Soils,  1904,  1905. 


TOPOGRAPHY. 


13 


Deposits  of  Pleistocene  and  Recent  age  form  a  nearly  con- 
tinuous mantle,  which  with  comparatively  few  exceptions  con- 
ceals the  hard  rocks  throughout  the  whole  of  the  area.  Only  the 
Southern  Highland,  the  Douglas  Range,  and  the  lake  cliffs  show 
many  rock  outcrops.  The  drift  deposits  range  in  thickness  from 
nothing  to  nearly  600  feet.  The  maximum  thickness  is  attained 
in  buried  valleys  under  the  St.  Louis  River  at  Superior  and 
south  of  Ashland,  and  in  the  Bayfield  Moraine. 

The  materials  of  the  drift  are  till,  clay,  sand,  and  gravel, 
nearly  always  of  red  or  yellow  color.  Water-laid  deposits  are 
more  abundant  than  ice-laid  material.  The  deeply  weathered 
character  of  the  rocks  at  most  points  suggests  that  glacial  ero- 
sion was  not  active,  at  least  toward  the  end  of  the  ice  epoch. 
Far  more  detailed  observations  than  any  heretofore  made  will 
be  needed  before  the  complex  history  of  these  deposits  is  made 
known.  The  question  of  the  origin  of  the  west  end  of  Lake 
Superior  is  considered  on  p.  95. 

At  one  stage  in  the  retreat  of  the  last  ice,  the  waters  of  Lake 
Superior1  stood  so  high  that  they  overflowed  through  a  low  col 
at  the  head  of  the  Brule  River,  at  an  elevation  of  some  500  feet 
above  the  present  level,  into  Lake  St.  Croix  in  Douglas  County. 
This  is  known  as  the  Lake  Duluth  stage.  The  outlets  of  the 
lower  stages,  whose  beaches  do  not  indicate  as  long  a  duration 
as  that  of  Lake  Duluth,  are  not  yet  definitely  known.  At  the 
present  time  a  slow  tilting  of  the  region  along  a  northwest- 
southeast  axis  is  going  on,  which  is  causing  the  water  to  advance 
upon  the  land  at  most  places  within  this  area,  the  movement 
probably  being  at  a  maximum  in  the  vicinity  of  Superior.  The 
large  amount  of  post-glacial  erosion  as  shown  by  the  deep 
stream  valleys,  is  due  to  the  impervious  character  of  the  soft  red 
clay  which  forms  the  surface  of  a  large  part  of  the  area. 


iA  brief  summary  of  this  subject  will  be  found  in  an  article  by 
Frank  Leverett,  Outline  of  History  of  the  Great  Lakes,  12th  report  of 
the  Michigan  Acad,  of  Sci.,  1910,  p.  19. 


14 


PREVIOUS  INVESTIGATIONS. 


CHAPTER  II 


PREVIOUS  INVESTIGATIONS 


Owen,  1847-50.  The  first  competent  geologists  to  make 
a  careful  examination  of  the  "Wisconsin  coast  of  Lake  Superior 
were  David  D.  Owen  and  his  assistants,  J.  G.  Norwood,  A. 
Randall,  arid  C.  Whittlesey.1  Their  explorations  were  made  be- 
fore the  completion  of  the  land  survey,  while  the  country  was 
still  known  as  the  Chippewa  Land  District.  This  survey  was 
made  for  economic  purposes,  since  the  question  of  the  disposal 
of  the  public  mineral  lands  was  then  a  vexed  one,  as  it  is  today. 
Owen  was  commissioned  by  the  Treasury  Department  to  classify 
the  public  lands  with  regard  to  their  mineral  and  agricultural 
value.  Taking  into  consideration  the  state  of  the  country,  and 
the  progress  of  the  science  of  geology  at  that  time,  this  piece 
of  work  was  remarkably  accurate  and  thorough.  The  party  ex- 
plored all  of  the  coast  and  most  of  the  streams,  mainly  during 
the  seasons  of  1847  and  1848. 

In  his  first  report,  in  1847,  Owen  concluded,  chiefly  from 
lithological  evidence,  that  the  Lake  Superior  sandstones  were 
post-Carboniferous,  for  he  regarded  all  the  igneous  rocks  as 
intruded  at  a  geologically  recent  date.  However,  in  his  final 
report  of  1852  he  withdrew  this  statement  and  advanced  the 

i  For  full  titles  with  annotations  refer  to  bibliography,  p.  21. 

Owen,  D.  D.,  Report  of  a  Geological  Reconnaissance  of  the  Chippewa 
Land  District,  Senate  Doc.  30th  Cong.,  1st  Sess.,  1847. 

Report  of  a  Geological  Survey  of  Wisconsin,  Iowa,  and  Minnesota, 
etc.    Philadelphia,  1852. 


PREVIOUS  INVESTIGATIONS. 


15 


hypothesis,  based  on  exposures  along-  St.  Croix  river,  that  it  was 
a  downward  continuation  of  the  Mississippi  valley  Cambrian 
He  drew  no  distinction  between  the  different  kinds  of  sandstone 
upon  the  lake.  Owen  also  noted  the  gentle  southeasterly  dip 
of  the  strata  in  the  Apostle  Islands,  and  along  the  south  coast, 
a  fact  which  has  escaped  many  subsequent  observers. 

Whittlesey,  1860.  In  1860  Charles  Whittlesey  explored  the 
eastern  part  of  this  district  but  owing  to  the  abolition  of  the 
Wisconsin  Geological  Survey  at  the  time  of  the  war,  his  report 
was  never  published.  An  article  entitled  "The  Penokee  Min- 
eral Range"  was  published  by  him  in  1863;  this  gives  a  brief 
description  of  the  district.1 

Irving,  1873-78.  Prof.  Roland  D.  Irving  was  the  first  geol- 
ogist to  study  the  complex  geology  of  the  Lake  Superior  region 
in  the  light  of  modern  knowledge.  The  eastern  half  of  the  dis- 
trict was  surveyed  under  the  personal  direction  of  Prof.  Irving, 
while  the  western  portion  was  covered  by  E.  T.  Sweet.  All  of 
the  known  outcrops  with  the  exception  of  those  of  Fish  Creek 
and  Oronto  River  were  visited.  The  main  fault  of  this  excel- 
lent piece  of  work  is  the  failure  to  show  the  outcrops  upon  the 
final  maps.  This  deficiency  is  supplied  in  part  from  the  text  of 
the  final  and  annual  reports ;  but  owing  to  the  destruction  of  the 
field  notes  by  fire,  it  is  a  serious  handicap  to  the  geologist  who 
attempts  to  retrace  the  work. 

Irving2  naturally  spent  most  of  the  short  time  at  his  disposal 
in  a  study  of  the  Penokee  Iron  District,  so  that  the  sandstones 
received  scant  attention.  Only  a  portion  of  the  outcrop  on 
Clinton  Point,  Iron  County,  was  visited ;  and  as  the  inclined  beds 
were  not  seen,  the  rock  was  correlated  with  the  horizontal  sand- 

1  Whittlesey,  Charles,  The  Penokee  Mineral  Range,  Proc.  Boston 
Soc.  of  Nat.  Hist.,  vol.  9,  pp.  235-44,  1863;  reprint  in  part,  Geol.  of  Wis., 
1873-9,  vol.  Ill,  p.  216. 

2  Irving,  R.  D.,  Some  Points  in  the  Geology  of  Northern  Wisconsin, 
Wis.  Acad,  of  Sci.  Trans.,  vol.  2,  1871,  pp.  107-119. 

  On  the  Age  of  the  Copper-Bearing  Rocks  of  Lake  Superior, 

etc.,  Amer.  Jour.  Sci.  and  Arts,  vol.  8,  1874,  pp.  46-56. 

—    Geol.  of  Wis.,  1873-9,  vol.  Ill,  pp.  1-24,  53-238. 

  Copper-Bearing  Rocks  of  Lake  Superior,  Mon.  U.  S.  Geol. 

Survey,  vol.  V,  1883;  see  references  below. 

F 


16 


PREVIOUS  INVESTIGATIONS. 


stcnes  of  the  islands.  In  his  preliminary  articles,  Irving  men- 
tioned horizontal  sandstone  and  shale  on  Silver  Creek  near  the 
modern  village  of  High  Bridge,  Ashland  County ;  hut  in  his  later 
monograph  he  stated  that  this  Avas  an  error  of  Lapham's.1 

In  the  Geology  of  Wisconsin,  Irving  affirmed  that  there  were 
two  great  unconformable  groups  of  sandstones.  This  statement 
was  based  first  upon  the  horizontal  attitude  of  the  Bayfield 
sandstone  group ;  second,  upon  the  supposed  unconformity  com- 
plicated by  slight  faulting  along  the  north  edge  of  the  Douglas 
Range ;  and  third,  upon  the  supposed  equivalence  shown  by  lith- 
ologic  and  structural  similarity  of  the  upper  group  to  the  Cam- 
brian (Eastern,  now  Jacobsville)  sandstone  of  Michigan.  There- 
fore the  Bayfield  group  (called  Western  by  Irving)  was  assigned 
to  that  period.  Irving  was  of  the  opinion  that  the  Bayfield 
Ridge  was  a  continuation  of  the  Douglas  Trap  Range,  although 
he  recognized  its  morainic  character. 

Sweet,  1873-77.  In  1873,  1875,  and  1877,  E.  T.  Swee;  made 
his  examinations  of  this  area  under  Irving  V  direction.  In  the 
last  year  he  made  a  trip  along  the  south  coast  of  Lake  Superior 
from  Ashland  to  Superior  in  the  short  space  of  two  weeks.2 
Sweet  was  unable  to  understand  the  contacts  of  the  traps  and 
sandstones  along  the  Douglas  Range  and  so  wisely  confined  him- 
self to  the  statement  that  the  sandstone  wTas  the  younger.  On 
Middle  River  he  mistook  the  horizontal  joints  for  bedding. 

Irving,  1881.  After  further  field  work  outside  of  Wiscon- 
sin, Irving  completed  a  report  upon  the  Copper  Bearing  Rocks 
of  Lake  Superior.3  Although  in  this  work  Irving  definitely 
asserted  the  existence  of  a  concealed  unconformity  between  the 
Bayfield  and  Oronto  groups,  he  conceded  that  on  structural 
grounds  there  was  no  reason  to  separate  this  upper  group  (called 


1  Irving,  R.  D.,  Copper-Bearing  Rocks  of  Lake  Superior,  Mon.  U.  S. 
Geol.  Survey,  vol.  V,  1883,  p.  411. 

2  Sweet,  E.  T.,  Some  notes  on  the  Geology  of  Northern  Wisconsin, 
Wis.  Acad,  of  Sci.  Trans,  vol.  3,  1876,  pp.  40-55. 

 Ann.  Rept.  Wis.  Gecl.  Survey,  1877,  p.  4. 

  Geol.  of  Wis.,  1873-9,  vol.  Ill,  pp.  305-362. 

s  Irving,  R.  D.,  Copper-Bearing  Rocks  of  Lake  Superior,  Mon.  U.  S. 
Geol.  Survey,  vol.  V,  1883. 


PREVIOUS  INVESTIGATIONS. 


17 


by  him  Western  Lake  Superior  sandstone)  from  the  underlying 
feldspathic  rocks,  since  both  should  be  horizontal  in  the  vicinity 
of  the  Apostle  Islands.1 

Winchell,  1872-99.  The  work  of  the  Geological  and  Natural 
History  Survey  of  Minnesota  was  carried  on  within  this  area  by 
N.  H.  Winchell.  The  final  report  was  published  in  18992  to- 
gether with  rather  large  scale  maps  showing  50  foot  contours. 
Unfortunately  these  maps  do  not  show  outcrops,  so  that  it  is 
often  difficult  to  see  the  basis  of  the  distinction  between  the  areas 
mapped  as  drift  and  those  where  the  underlying  formations  are 
shown.  Moreover,  there  are  several  serious  errors  in  the  draft- 
ing of  the  sheets  covering  the  vicinity  of  Duluth.  J 

Local  details  were  published  from  time  to  time  in  the  annual 
reports,  and  in  1895  Winchell  published  two  articles  which  de- 
serve especial  attention.3    These  were  of  a  distinctly  controver- 
sial nature  but  many  of  the  points  were  essentially  sound.  He 
described  the  conglomerates  of  trre  St.  Louis  River  and  divided 
them  into  two  parts.    The  lower  quartz  pebble  conglomerate  he 
placed  at  the  base  of  the  Keweenawan,  and  the  remainder,  which 
contains  trap  pebbles,  as  contemporaneous  with  the  last  erup- 
tions.   This  involves  the  assumption  tlrat  an  unconformity  ex- 
ists within  the  space  of  a  few  feet  where  the  exposure  happens 
to  be  covered  by  debris.    He  correctly  argued  that  the  mere 
presence  of  trap  pebbles  in  a  conglomerate  does  not  imply  a  post- 
Keweenawan  age,  since  such  pebbles  are  found  in  all  Keween- 
awan detrital  rocks.    In  other  words,  folding  and  erosion  must 
have  gone  on  simultaneously  with  the  deposition  of  sediments 
in  other  places.    Winchell  also  threw  some  doubt  upon  the  un-  • 
conformity  supposed  by  Irving  to  exist  along  the  Douglas  Range, 
suggesting  that  some  of  the  conglomerate  might  be  faulted  up 
from  lower  horizons.    In  the  second  article  entitled,  "A  Rational 
View  of  the  Keweenawan,''  Winchell  formulated  the  following 
series  of  objections  to  Irving 's  view  as  to  the  unconformity  of 
the  two  sandstone  groups.    Although  his  object  was  to  demon- 


1  Irving,  R.  D.,  Ibid,  pp.  154,  258,  365,  410,  plate  XXVIII. 

2  Winchell,  N.  H.,  Geology  of  Minnesota,  1872-99,  vol.  IV,  pp.  1-24, 
212-225,  550-580. 

s  Winchell,  N.  H.,  Crucial  Points  in  the  Geology  of  the  Lake  Superior 
Region,  Amer.  Geologist,  1895,  vol.  16,  pp.  75,  150. 
2 


18 


PREVIOUS  INVESTIGATIONS. 


strate  that  the  entire  Keweenawan  was  of  Cambrian  age,  a  ques- 
tion not  considered  by  the  present  writer,  it  is  worth  while  to 
quote  these  objections: 

There  is  no  permanent  petrographic  distinction  between  them  [the 
two  sandstone  groups  J.  The  red  shale  and  red  sandstone,  which  are 
said  to  prevail  in  the  tilted  beds  [Oronto  group],  are  found  in  great 
volume  in  the  lower  portion  of  the  horizontal  beds  [Bayfield  group]. 
This  may  be  seen  by  consulting  the  sections  of  the  horizontal  beds 
[along  St.  Louis  River]    *    *  *. 

The  tilted  beds  [Oronto  group]  are  sometimes  horizontal,  and  the 
horizontal  beds  [Bayfield  group]  are  sometimes  tilted  at  high  angles. 
[The  author  did  not  state  the  localities  where  this  paradox  is  true.] 

The  top  of  the  Keweenawan  sandstones  has  never  been  observed. 

The  bottom  of  the  overlying  [Bayfield]  sandstones  has  never 
been  observed  except  where,  by  regional  subsidence,  it  is  non-conform- 
able upon  the  iilted  traps  or  the  older  rocks.  [It  may  be  noted  that 
all  known  contacts  with  the  traps  are  complicated  by  faulting.] 

In  various  places  the  horizontal  sandstone  [of  the  Mississippi  valley], 
even  some  of  the  higher  magnesian  limestones  [no  such  case  is  known 
to  the  writer],  have  been  seen  non-conformable  on  the  traps  of  the 
lower  portion  of  the  Keweenawan,  indicating  a  progressive  subsi- 
dence after  the  tilting  of  the  traps. 

The  non-conformable  contact  which  is  assumed  to  have  taken  place 
between  the  base  of  the  horizontal  sandstones  [Bayfield  group]  and 
.the  Keweenawan  tilted  sandstones  [Oronto  group]  has  never  been 
observed. 

The  whole  region  in  which  this  question  centers  is  one  of  disturb- 
ance and  eruptive  action.  Even  since  some  of  the  horizontal  sand- 
'stones  were  deposited  there  have  been  such  movements  [along  the 
Douglas  and  Keweenaw  Point  faults]  that  the  sandstones  are  broken 
and  thrust  in  various  attitudes  in  their  relation  to  the  trap. 

The  shortest  observed  interval  between  the  horizontal  and  the  tilted 
sandstones  within  which  such  nonconformity  must  exist,  if  it  exist 
at  all,  is  four  miles,  Viz.,  between  Montreal  River  and  Clinton  Point.i 

If  it  were  to  be  affirmed  that  there  ins  no  such  non-conformable  con- 
tact between  these  sandstones,  the  statement  could  not  be  disproved  by 
any  known  facts. 

If  the  statement  were  to  be  made  that  the  upper  part  of  the  Ke- 


i  The  sandstones  of  Clinton  Point  are  not  horizontal  and  do  not  be- 
long to  the  Bayfield  group  (see  p.  55). 


PREVIOUS  INVESTIGATIONS. 


19 


weenawan  [Oronto]  sandstones  passes  conformably  into  the  horizontal 
*    *    *    [Bayfield]  sandstones    *    *    *    in  all  places  where  they 
are  in  contact,  such  statement  could  not  he  disproved  by  any  known 
facts,  but  would  be  in  harmony  with  all  that  is  known  of  the  formation. 

A  figure  given  by  Winchell  showing  a  generalized  section  from 
Montreal  River  to  Clinton  Point  may  be  mentioned,  for  the  fact 
that  it  shows  horizontal  sandstone  on  Silver  Creek  in  Ashland 
County,  indicating  that  the  author  had  overlooked  Irving 's  de- 
nial of  the  existence  of  such  a  formation  (see  p.  16). 

In  his  final  report  of  1899,  Winchell  expressed  his  opinion, 
based  on  the  boring  at  Short  Line  Park  near  Duluth,  that  the 
sandstone  of  St.  Louis  River  was  deposited  contemporaneously 
with  the  later  igneous  eruptions,  the  gradual  dying  out  of  which 
"  rendered  the  sandstone  more  and  more  siliceous,"  so  that 
' '  the  upper  strata  are  almost  free  from  the  shaley,  red  sediment 
which  characterizes  the  lower  portion."    It  was  also  stated  that 
the  sandstones  here  found  are  conformable  beneath  those  of 
known  Upper  Cambrian  age  in  the  Mississippi  valley.    This  con- 
clusion was  apparently  based,  although  the  evidence  is  nowhere 
clearly  exposed,  upon  the  apparent  areal  connection  of  the  sand- 
stones of  the  Lake  Superior  and  Mississippi  basins.    The  results 
of  deep  drilling  at  Stillwater1  and  other  points  in  southeastern 
Minnesota  showing  a  thick  red  sandstone  series  beneath  the  hor- 
izontal Cambrian,  were  also  cited  as  supporting  the  conten- 
tion that  there  was  a  complete  and  conformable  transition  be- 
tween the  Upper  Cambrian  and  the  Keweenawan  traps. 

Grant,  1899-1900.  In  1899  Professor  U.  S.  Grant  of  North- 
western University  commenced  a  study  of  the  Keweenawan 
traps  of  Wisconsin  which  were  then  being  prospected  for  cop- 
per, as  they  have  been  at  intervals  of  thirty  or  forty  years  ever 
since  first  discovered.  After  a  slight  amount  of  work  in  1900 
the  survey  was  discontinued  and  the  notes  were  never  published 
in  full.  Much  of  this  valuable  material  has  been  made  use  of 
by  the  writer  for  the  first  time.2 


1  Winchell,  N.  H.,  Natural  Gas  in  Minnesota.  Minn.  GeoJ.  &  Nat. 
Hist.  Survey,  Bull.  V,  1889,  p.  25. 

2  Grant,  U.  S.,  Preliminary  Report  on  Copper-Bearing  Rocks  of  Doug- 
las County,  Wis.  Geol.  and  Nat.  Hist.  Survey,  Bull.  VI,  1900,  2nd  ed. 
1901. 


20 


PREVIOUS  INVESTIGATIONS. 


In  his  report  Grant  did  not  touch  upon  the  age  of  the  sand- 
stones, but  in  a  later  paper1  he  described  the  contacts  which 
occur  within  the  area  he  studied.  He  recognized  the  great  amount 
of  faulting  which  has  taken  place  since  the  deposition  of  the 
sandstone,  as  shown  by  the  fold  on  Middle  River.  At  this  place 
he  perceived  the  true  bedding,  but  assumed  that  the  structure 
was  anticlinal  as  he  did  not  observe  the  ripple  marks  which 
conclusively  demonstrate  the  overturning  of  the  strata.  He  saw 
that  the  great  Douglas  fault  was  of  the  thrust  type  although 
he  showed  it  as  vertical  on  his  structure  sections.  The  evidence 
with  regard  to  the  unconformity  along  this  fault  he  declared  to 
be  inconclusive. 

Collie,  1900.  In  1900  Prof.  G.  L.  Collie  of  Beloit  College, 
visited  the  region  about  Bayfield  and  made  some  steamer 
trips  through  the  Apostle  Islands.  A  paper2  published  by  him 
describes  mainly  the  physiography  of  the  region.  His  obser- 
vations of  the  Lake  Superior  sandstones  were  very  meager,  while 
the  theoretical  conclusions  as  to  the  geological  history  of  the 
region  are  for  the  most  part  based  upon  misconceptions  of  the 
facts. 

Hall,  1901-08.  In  1901  Prof.  C.  W.  Hall  of  the  University 
of  Minnesota  described  the  Keweenawan  area  of  the  eastern  part 
of  that  state.3  Evidence  was  cited  to  show  that  the  great  fault 
of  Douglas  County  extends  far  into  Minnesota,  but  the  sections 
are  drawn  on  such  an  exaggerated  vertical  scale  that  the  true 
relations  are  confused. 

In  1908,  Hall  prepared  a  paper  discussing  the  great  series 
of  red  sandstones  and  shales  which  drill  holes  have  discovered 
beneath  the  exposed  Paleozoic  rocks  of  southern  Minnesota. 
These  he  stated  to  be  conformable  beneath  the  later  sediments 
and  to  represent  a  transition  between  the  Paleozoic  and  Algon- 


1  Grant,  U.  S.,  Junction  of  Lake  Superior  Sandstone  and  Keweenaw- 
an Traps  in  Wisconsin,  Bull.  Geol.  Soc.  Amer.,  vol.  13,  1902,  p.  6. 

2  Collie,  G.  L.,  Wisconsin  Shore  of  Lake  Superior,  Bull.  Geol.  Soc. 
Amer.,  vol.  12,  1901,  p.  199. 

3  Hall,  C.  W.,  Keweenawan  Area  of  Eastern  Minnesota,  Bull.  Geol. 
Soc.  Amer.,  vol.  12,  1901,  p.  313. 


PREVIOUS  INVESTIGATIONS. 


21 


kian  rocks.  Unfortunately  this  paper  was  never  published,  an 
abstract  only  appearing  in  Science.1 

Lane,  1908.  In  1908  Professors  A.  C.  Lane,  then  state  geol- 
ogist of  Michigan,  and  C.  K.  Leith  and  Lawrence  Martin  of  the 
University  of  Wisconsin,  visited  Clinton  Point  and  parts  of 
Montreal  and  Oronto  rivers.  They  first  observed  some  of  the 
inclined  beds  at  the  former  locality,  Professor  Lane  giving  it  as 
his  opinion  that  they  are  conformable  upon  the  formations  seen 
to  the  southeast.2  It  was  suggested  that  a  fault  parallel  to  that 
on  Keweenaw  Point  might  pass  through  the  belt  of  no  expo- 
ures  found  on  Montreal  River  and  thus  give  an  apparent  thick- 
ness of  sandstone  much  in  excess  of  the  fact. 

Grout,  1910.  The  work  of  Professor  Hall  in  Minnesota  has 
been  carried  further  by  Professor  F.  P.  Grout  of  the  University 
of  Minnesota.  "Writing  in  1910,  he  gave  a  summary  of  the  re- 
cent work.3  He  expressed  some  doubt  as  to  the  correlation  of 
the  sandstones  north  of  the  Douglas  fault  with  the  fossiliferous 
series  of  the  St.  Croix  valley  which  overlie  the  tilted  traps  with 
evident  unconformity.  The  areal  connection  is  moreover 
doubted  since  a  wide  drift-covered  interval  occurs  between  the 
two  areas  of  sandstone. 

BIBLIOGRAPHY 

Buckley,  E.  R.,  On  the  Building  and  Ornamental  Stones  of  Wiscon- 
sin, Wis,  Geol.  &  Nat.  Hist.  Survey,  Bull.  IV,  1898. 
Describes  quarries. 

Case,  E.  C,  Wisconsin,  Its  Geology  and  Physical  Geography,  Hendee, 
Bamford,  Crandall  Co.,  Milwaukee,  1907. 
A  compiled  work  describing  the  geography  of  region  in  some  detail. 

1  Hall,  C.  W.,  The  Red  Sandstone  Series  of  Southeastern  Minnesota, 
Abstract.    Science,  vol.  27,  1908,  p.  722. 

2  Lane,  A.  C.  &  Seaman,  A.  113.,  The  Geological  Section  of  Michigan. 
Rept.  State  Board  of  Geol.  Survey  of  Michigan  for  1908,  p.  23.  A  brief 
reprint  is  found  in  Journal  of  Geology,  vol.  13,  1907,  p.  680. 

s  Grout,  F.  F.,  Contribution  to  the  Petrography  of  the  Keweenawan, 
Journ.  Geol.,  vol.  18,  1910.  p.  633. 
Personal  communications. 


22 


PREVIOUS  INVESTIGATIONS. 


Chamberlin,  T.  C.,  Geology  of  Wisconsin,  Survey  of,  1873-79,  Vol.  I, 
pp.  119-137. 
General  conclusions  of  the  work  of  Irving. 

Collie,  G.  L.,  The  Wisconsin  Shore  Line  of  Lake  Superior,  Bull.  Geol. 
Soc.  of  America,  vol.  XII,  1901,  p.  199. 
Describes  the  sandstones  briefly. 

Grant,  U.  S.,  Preliminary  Report  on  the  Copper-bearing  Rocks  of 
Douglas  County,  Wisconsin,  1st  edition  1900;  2nd  edition  1901,  contains 
a  preliminary  report  on  the  copper-bearing  rocks  of  Washburn  and  Bay- 
field Counties.    Wis.  Geol.  &  Nat.  Hist.  Survey,  Bull.  VI,  1900,  1901. 

 ,  Junction  of  the  Lake  Superior  Sandstone  and  Keweenawan 

Traps  in  Wisconsin.    Bull.  Geol.  Soc.  of  America,  vol.  XIII,  1902,  p.  6. 
A  short  description  of  the  several  contacts.  Advances  no  definite  conclusions. 

Grout,  F.  P.,  A  contribution  to  the  Petrography  of  the  Keweenawan, 
Jour,  of  Geology,  vol.  XVIII,  1910,  pp.  633-657. 
Mentions  sandstones  briefly  and  gives  map  of  exposures  in  Minnesota. 

Hall,  C.  W.,  Keweenawan  Area  of  Eastern  Minnesota,  Bull.  Geol.  Soc. 
of  America,  vol.  XII,  1901,  p.  313. 
Gives  maps  and  sections  and  describes  general  structure  of  region. 

 ,  The  Red  Sandstone  Series  of  Southeastern  Minnesota. 

Unpublished  paper,  not  available.  Abstract,  Science,  new  ser.  vol.  27,  1908,  p.  722. 

Hall,  C.  W.,  Meinzer,  O.  E.,  and  Fuller,  M.  L.,  Geology  and  Under- 
ground Waters  of  Southern  Minnesota,  U.  S.  Geological  Survey,  Water 
Supply  Paper  256,  1911 
Describes  the  pre-Potsdam  red  clastic  rocks  of  Minnesota. 

Irving,  R.  D.,  On  Some  Points  in  the  Geology  of  Northern  Wisconsin, 
Wis.  Acad,  of  Science  Transactions,  vol.  II,  1874,  p.  107. 

 ,  On  the  Age  of  the  Copper-bearing  rocks  of  Lake  Superior;  and 

On  the  Continuation  of  the  Lake  Superior  Synclinal,  Am.  Journ.  of  Sci. 
and  Arts,  3rd  series,  vol.  VIII.  1874,  p.  46. 

 ,  Geology  of  Wisconsin,  Survey  of  1873-9  (T.  C.  Chamberlin  in 

charge) : 

General  Geology  of  the  Lake  Superior  Region,  vol.  Ill,  pp. 

1-24. 

Geology  of  the  Eastern  Lake  Superior  Region,  vol.  Ill,  pp. 

53-238. 

.  1  The  Copper-bearing  Rocks  of  Lake  Superior,  Monographs  of 

the  U.  S.  Geological  Survey,  vol.  V,  1883. 


PREVIOUS  INVESTIGATIONS. 


23 


Irving,  R.  D.,  On  the  Classification  of  the  Early  Cambrian  and  Pre- 
Cambrian  Formations,  7th  Ann.  Rept.  of  the  Director  of  the  U.  S. 
Geological  Survey  to  the  Secretary  of  the  Interior,  1885-86,  1888,  p.  412. 
Discusses  correlation  of  the  sandstones. 

Irving,  R.  D.,  and  Chamberlin,  T.  C,  Observations  on  the  Junction  of 
the  Eastern  Sandstone  and  the  Keweenaw  Series  on  Keweenaw  Point, 
Lake  Superior,  U.  S.  Geological  Survey,  Bull.  23,  1885. 
Refers  briefly  to  sandstones  of  Wisconsin. 

Krey,  J.,  Lake  Superior  and  Mississippi  Canal.    Letter  from  the 

Sec'y  of  War  transmitting    *    *    *    Report  of  Examination  of  Survey 

of  a  Canal  Connecting  Lake  Superior  and  Mississippi  River.  House 

Exec.  Document  330,  54th  Cong.,  1st  session,  1896. 

Gives  results  of  a  preliminary  survey  of  Brule  River,  with  a  few  elevations  and  gen- 
eral maps. 

Lane,  A.  C,  and  Seaman,  A.  E.,  Notes  on  the  Geological  Section  of 

Michigan,  Rept.  of  the  State  Board  of  Geological  Survey  of  Michigan 

for  the  year  1908,  p.  23. 

Reprint  Jour,  of  Geol.,  vol.  XV,  1907,  p.  680.  Describes  exposure  in  vicinity  of  Mon- 
treal River,  giving  names  to  the  sandstones. 

Leverett,  P.,  Outline  of  History  of  the  Great  Lakes,  12th  Rept.  of 
Michigan  Academy  of  Science,  1910,  p.  19. 

Meads,  A.  D.,  The  Stillwater  Deep  Well,  Bull.  Minn.  Acad,  of  Nat. 
Sci.,  vol.  3,  No.  2,  1891,  p.  274. 
First  published  in  Amercan  Geologist,  vol.  3,  1889,  p.  342. 

Owen,  D.  D.,  Report  of  a  Geological  Reconnaissance  of  the  Chippewa 
Land  District  of  Wisconsin,  etc.  Senate  Exec.  Document  No.  59,  30th 
Cong.,  1st  session,  18  47,  vol.  VII,  pp.  49-85. 

— — ,  Report  of  a  Geological  Survey  of  Wisconsin,  Iowa  and  Minn- 
esota, etc.,  made  under  instructions  from  the  U.  S.  Treas.  Dept.  Lip- 
pincott,  Gambo  &  Co.,  Philadelphia,  1852. 

Sweet,  E.  T.,  Some  Notes  on  the  Geology  of  Northern  Wisconsin, 
Wisconsin  Acad,  of  Science,  Transactions,  vol.  Ill,  1876,  pp.  40-55. 

 ,  Annual  Report  of  Wis.  Geol.  Survey  for  the  year  1877,  p.  4. 

 ,  Geology  of  Wisconsin,  Survey  of  1873-9,  Geology  of  the  West- 
ern Lake  Superior  District,  vol.  Ill,  pp.  305-362. 

Winchell,  N.  H.,  Natural  Gas  in  Minnesota.    Minn.  Geol.  &  Nat.  Hist. 
Survey,  Bull.  V,  1889,  pp.  25,  31. 
pescribes  drill  holes  at  Short  Line  Park  and  Stillwater. 


24 


PREVIOUS  INVESTIGATIONS. 


 ,  Geological  and  Natural  History  Survey  of  Minn.,  10th  Ann. 

Report  for  the  year  1881,  pp.  9,  10,  30-33. 
Gives  sections  on  St.  Louis  River. 

 ,  Id,  23rd  Ann.  Rept.  for  the  year  1S94,  p.  239. 

Describes  conglomerates  near  St.  Louis  River. 

 ,  Crucial  Points  in  the  Geology  of  the  Lake  Superior  Region; 

The  Keweenawan  According  to  the  Wisconsin  Geologists.  American 
Geologist,  vol.  XVI,  1895,  p.  75. 
Criticises  Irving's  views. 

 ,  Crucial  Points  in  the  Geology  of  the  Lake  Superior  Region;  A 

Rational  View  of  the  Keweenawan.  American  Geologist,  vol  XVI, 
1895,  p.  150. 

Discusses  objections  to  the  separation  of  Keweenawan  and  Lake  Superior  sand- 
stones. 

 ,  The  Geology  of  Minnesota,  vol.  IV  of  the  Final  Report,  1899: 

Geology  of  Carlton  County,  pp.  1-24. 

Geology  of  the  Southern  Portion  of  St.  Louis  County,  pp. 
212-221. 

Geology  of  the  Carlton  Plate,  pp.  550-565. 
Geology  of  the  Duluth  Plate,  pp.  566-580. 

Whittlesey,  C.,  The  Penokee  Mineral  Range,  Proc.  Boston  Soc.  of 

Nat.  Hist.,  vol.  IX,  1863,  pp.  235-244. 

 ,  Summary  of  above,  in  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  216. 

Gives  general  summary  of  the  region  and  mentions  the  southeasterly  dip  of  the 
rocks  in  the  Apostle  Islands. 

U.  S.  Dept.  of  Agric,  Bureau  of  Soils,  Soil  Survey  of  the  Superior 
Area  of  Wisconsin.  T.  A.  Caine  and  W.  S.  Lyman,  Field  Operations  of 
the  Bureau  of  Soils,  1904. 

 ,  Soil  Survey  of  the  Carlton  Area.  Minnesota-Wisconsin,  W.  J. 

Geib  and  G.  R.  Jones.    Id.,  1905. 

Van  Hise,  C.  R.,  Leith,  C.  K„  [and  Martin,  L,],  Geology  of  the  Lake 
Superior  Region,  Mon.  of  U.  S.  Geol.  Survey,  vol.  LII,  1911. 
Gives  summary  of  geology  and  physiography  up  to  date. 


BAYFIELD  GROUP. 


25 


CHAPTER  HI 


THE  BAYFIELD  SANDSTONE  GROUP 


Limits  of  the  Group.  The  sandstones  found  along  the  Wis- 
consin coast  of  Lake  Superior  have  long  been  divided  into  two 
groups.  It  is  possible  to  draw  a  fairly  definite  line  at  the  base 
of  the  prevailing  quartz  sandstones  known  as  the  Bayfield  group, 
separating  them  from  the  underlying  arkose  sandstones  and  red 
shales  which  will  hereafter  be  termed  the  Oronto  group  and 
which  will  be  described  in  Chapter  IV.  The  Bayfield  group  was 
formerly  known  as  the  Western  Lake  Superior  sandstone.  Be- 
cause the  correlation  with  the  Lake  Superior  sandstone  group 
of  Michigan  is  uncertain,  it  seemed  best  to  give  the  rocks  in 
Wisconsin  a  new  name. 

Areal  Extent.  The  Bayfield  group  is  the  highest  rock  form- 
ation of  the  area  studied.  It  is  the  uppermost  rock  of  all  of  the 
coast  and  islands  from  the  mouth  of  Fish  Creek  at  the  head  of 
Chequamegon  Bay  to  the  west  line  of  the  state;  inland  it  is 
bounded  by  the  Douglas  Trap  Range  so  that  it  underlies  all  of 
the  Western  Plain;  how  much  of  the  Bayfield  Ridge  is  under- 
lain by  sandstone  is  unknown  on  account  of  the  heavy  drift.  So 
far  as  known,  it  never  rises  more  than  about  400  feet  above  the 
lake.  The  strata  are,  over  most  of  this  area,  gently  inclined  to  the 
southeast  at  low  angles  with  a  maximum  of  about  five  degrees. 
Apparently  this  dip  decreases  towards  the  southeast.  Locally 
considerable  folds  are  found  (see  p.  62),  which  bring  to  the  sur- 
face rocks  believed  to  belong  to  the  underlying  Oronto  group. 
The  Bayfield  group  extends  into  Minnesota  and  may  possibly  run 


26 


BAYFIELD  GROUP. 


beneath  the  Upper  Cambrian  sandstones,  but  its  relations  to 
them  are  as  yet  unknown. 

Subdivisions.  The  present  study  has  shown  that  the  Bay- 
field group  as  seen  in  Wisconsin  may  be  divided  into  the  follow- 
ing formations,  beginning  at  the  top ; 

Approximate  thickness 
Chequamegon  Sandstone.    Red  and  white  sandstone 
composed  predominantly  of  quartz  grains,  with 

thin  lenticular  beds  of  red  sandy  shale   1,000  feet 

Devils   Island   Sandstone.     Pink   and   white  pure 

quartz  sandstone  with  abundant  ripple  marks   300 

Orienta  Sandstone".  Like  the  Chequamegon  in  its 
upper  part,  but  containing  more  feldspar  grains 
especially  towards  the  base   3,000 


Total  thickness,  about    4,300  feet 

Composition.  Although  predominantly  a  red  sandstone,  the 
Bayfield  group  is  not  wholly  of  that  color.  In  many  beds,  and 
throughout  most  of  the  Devils  Island  formation,  lighter  colors 
prevail,  ranging  from  pink,  through  yellow  and  light  brown  to 
gray  and  white.  The  very  dark  red  "  brownstone, ' '  widely 
known  as  a  building  stone,  comprises  only  a  small  part  of  the 
group. 

In  size  of  grain  the  rocks  vary  from  coarse  pebbly  grits  down 
to  shales,  although  very  little  fine  clay  occurs.  (See  Plates 
TIT,  p.  26,  and  VI,  p.  44).  The  coarse  grits1  are  usually  the 
lightest  colored  beds,  and  the  thin  bedded  fine  grained  layers 
are  usually  the  darkest  in  tint.  The  size  of  grain  often  varies 
very  rapidly,  but  is  usually  coarsest  near  to  bedding  planes.  The 
cement  is  generally  quartz ;  the  iron  oxide,  even  where  abundant, 
not  being  important  as  a  cementing  material.  The  iron  usu- 
ally coats  the  surfaces  of  the  grains.  Crystal  faces  due  to  en- 
largement of  quartz  grains,  which  are  often  so  conspicuous  in  the 
sandstones  of  southern  Wisconsin,  are  seldom  observed.  Enlarge- 
ments of  grains  are  nevertheless  common  but  are  nearly  always 
quite  irregular  in  form.    The  degree  of  rounding  of  the  grains  is 

i  In  the  use  of  the  term  "grit",  the  writer  returns  to  its  original 
meaning,  a  rocit  intermediate  between  sandstone  and  conglomerate. 


Wis.  Geol.  and  Nat.  Hist.  Survey.  Bulletin  No.  XXV,  Plate  III. 

Photomicrographs  in  Ordinary  Light,  Magnified  12  Diameters.  (Buckley, 
Bull.  IV,  Plate  LXV). 


A 


B 


A.  Chequamegon  sandstone  from  quarry  at  Houghton,  Bayfield  County  (speci- 
men 4719).  The  light-colored  grains,  averaging  .35  mm.  in  diameter,  are  quartz, 
and  show  irregular  secondary  enlargements,  which  have'  accentuated  their  angu- 
larity. The  gray  grains  are  mainly  somewhat  decomposed  feldspars,  and  the 
black  areas  are  ferric  oxide. 


B.  Chequamegon  sandstone  from  quarry  on  Basswood  Island  (specimen  4714). 
In  this  section,  the  grains  are  somewhat  more  rounded  than  in  A.  Feldspar  is 
not  as  abundant.    The'  grains  run  up  to  .40  mm.  in  diameter. 


BAYFIELD  GROUP. 


27 


variable,  the  best  rounded  grains  being  those  of  the  Devils 
Island  formation,  while  in  the  other  formations  the  grains  are 
usually  subangular.1  They  contrast  sharply  with  the  smooth 
grains  of  the  sandstones  in  .southern  Wisconsin  (see  p.  101). 

The  materials  of  the  sandstones  of  the  Bayfield  group  are  in 
order  of  abundance:  quartz,  feldspars  (both  orthoclase  and  plag- 
ioclase),  micas,  iron  oxides  (both  magnetite  and  limonite), 
chert,  and  ferromagnesian  minerals.  Often  the  materials  other 
than  quartz  comprise  nearly  one-fourth  of  the  rock.  Most  of 
these  minerals  are  end  products  of  weathering,  so  that  the  rock  is 
very  resistant  to  the  action  of  the  atmosphere.  The  feldspars, 
however,  are  nearly  always  somewhat  decomposed,  and  in  the 
more  porous  sandstones  have  often  been  weathered  into  little 
specks  of  white  kaolin.  It  appears  probable  that  a  large  part  of 
the  decomposition  has  taken  place  since  the  deposition  of  the 
rock,  since  otherwise  the  forms  of  the  grains  would  not  have  been 
preserved  so  perfectly.  Sometimes  sands  largely  composed  of 
magnetite  grains  occur.  The  Devils  Island  formation  is  an  ex- 
ception to  the  most  part  of  the  group  in  being  nearly  pure 
quartz  sandstone,  of  medium  to  fine  grain. 

The  following  chemical  analyses  confirm  the  results  obtained 
by  the  examination  of  thin  sections  (Plates  III,  p.  26,  and  VI, 
p.  44).  The  amount  of  feldspar  is  considerable  and  appears  to 
be  greater  in  the  lower  members  of  the  group. 


i  Irving,  R.  D.,  Geol.  of  Wisconsin,  1873-7Q,  vol.  Ill,  p.  207. 
Buckley,  E.  R.,  Building  and  Ornamental  Stones  of  Wisconsin,  Wis. 
Geol.  and  Nat.  Hist.  Survey,  Bull.  IV,  p.  172.  s 

Note:  It  is  this  angularity  of  the  grains  which  makes  the  sands  de- 
rived from  the  sandstone  valuable  for  concrete.  Lake  sands  washed 
from  the  drift,  like  those  of  Minnesota  Point,  are  much  more  rounded 
and  hence  less  desirable.    (See  p.  11.) 


28  BAYFIELD  GROUP. 

ANALYSES  OF  SANDSTONES  OF  THE  BAYFIELD  GROUPi 


CHEQUAMEGON SANDSTONE 


Locality 

86.57 
87.02 
89.76 
91.64 
93.50 

m 

o 
< 

Q 

03 
fa 

CaO 

It 

O 

si 

Li 

o 

ct 

z 

c 

Total 

8.43 
7.17 

1.55 
3.91 

2.36 
1.43 

.67 
.22 

T 

99.58% 
99.92% 

.11 

not 
not 
MgC 

.06 

g  i  ven 
given 

Os- 

T 

3.  Basswood  Id  

4.  Hermit  Id  



3.90 

(Ca, 



1.00) 

98.40 

ORIENT  A  SANDSTONE 


6.  Port  Wing  

89.33  6.05 
90.86  4.76 
84.13  

1.41 

1  58 

T 
.15 
not 

T 
.59 
given 

2.12 
1  06 

.59 
.45 

99.50 
99/45 

7.  Siskowit  Pt  

8.  Eagle  Id  

'  1 

Shale  Beds.  Small  lenticular  beds  of  shale,  seldom  over 
five  feet  in  thickness,  are  found  throughout  the  Chequamegon  and 
Orienta  sandstones.  These  are  almost  wholly  of  a  sandy,  mica- 
ceous character,  little  fine  clay  being  found.  In  color  they  are 
usually  the  darkest  parts  of  the  rock,  being  a  deep  red  tint,  but 
are  almost  always  streaked  or  spotted  with  yellow  or  white ;  less 
commonly,  gray  and  green  sandy  shales  are  found.  A  very  fre- 
quent accompaniment  of  these  beds  is  a  few  inches  of  yellowish, 
coarse,  and  often  pebbly  sandstone  above  or  below,  or  on  both 
sides  of  the  red  bed.  Sometimes  pebbles  occur  in  the  shale  it- 
self. The  shale  beds  are  most  common  in  hollows  or  troughs  in 
the  bedding,  less  often  on  inclined  bedding  planes  (Fig.  1). 
Their  horizontal  extent  is  always  small;  they  either  pinch  out 
or  grade  into  thin  bedded  sandstone  or  curve  up  so  that  the  lay- 
ers are  cut  off  by  the  overlying  sandstone  bed. 

i  Nos.  2,  3,  4  and  8  by  E.  T.  Sweet,  Geol.  of  Wis.,  vol.  Ill,  p.  208.  Nos. 
1  and  6  by  W.  W.  Daniells,  Wis.  Geol.  and  Nat.  Hist.  Survey,  Bull.  IV, 
p.  420.  No.  7,  Geol.  of  Minnesota,  vol.  I,  pp.  200,  202.  No  5,  by  J.  G. 
Norwood,  Chippewa  Land  District,  1847,  p.  56;  Geol.  Survey  of  Wis., 
etc.,  1852,  p.  188. 


BAYFIELD  GROUP. 


29 


Bedding.  As  a  whole,  the  Bayfield  group  is  very  irregu- 
larly bedded,  in  contrast  to  the  even  bedded  calcareous  sand- 
stones of  southern  Wisconsin.  This  fact  makes  it  hard  to  de- 
scribe the  features  satisfactorily.  The  individual  beds  range  in 
thickness  from  a  fraction  of  an  inch  to  over  twenty  feet,  but 
within  these  massive  beds  are  minor  bedding  planes  which  are 
more  evident  on  natural  exposures  than  in  the  quarries.  The 


.  3  feet  . 

Fig.  1.    Bedding  in  Orienta  sandstone',  Siskowit  Pt,  Bayfield  County. 

most  striking  and  interesting  feature  of  the  bedding  is  what  may 
be  called  "down  curves."  These  are  usually  seen  only  in  cross 
section  so  that  their  character  in  three  dimensions  can  not  be  ob- 
served. They  may  be  sections  of  curved  cross  bedding,  or  actual 
troughs.  In  width  they  range  up  to  200  feet,  but  most  are  of 
far  less  size.  Two  of  the  clearest  seen  are  shown  in  Plate  IV, 
p.  30,  and  Fig.  2.  The  first  shown  is  not  over  twenty-five  feet 
across  and  is  filled  with  curved  beds.  Sometimes  the  filling  is 
a  bed  of  red  shale,  or  beds  of  horizontal  sandstone,  usually  thin- 


lfoot 


Fig.  2.    Channel  in  sandstone  layers — Quarry  northeast    of  Washburn,  Bay- 
field County. 

ner-tedded  than  the  rock  below.  Oftentimes  the  relation  of  the 
down  curve  to  the  underlying  rock  is  not  clear;  but  in  the  in- 
stance shown  in  Plate  IV,  B,  the  underlying  rock  is  cross 
bedded ;  here  it  is  seen  that  the  depression  cuts  through  the  pre- 
viously deposited  layers.  In  other  instances  the  down  curve  ap- 
pears to  be  an  actual  bend  in  the  bedding. 

The  origin  of  these  interesting  features  is  thought  to  be  in 
part  curved  cross  bedding  (cf.  p.  30)  and  in  part  erosion  by 


30 


BAYFIELD  GROUP. 


streams  or  currents  of  beds  previously  deposited.  In  this  case 
the  hypothesis  of  subaerial  origin  of  the  formation  is  favored. 
The  great  diversity  of  forms,  often  incomplete  in  development, 
leads  one  to  think  that  different  agencies  caused  the  various 
forms. 

A  less  common  feature  is  an  upward  bending  of  the  strata 
as  shown  in  Plate  I,  B,  frontispiece,  and  Fig.  3.  Sometimes 
even  sharper  forms  occur,  but  most  are  comparatively  gentle 
domes  or  ridges. 

Cross  bedding  is  very  common,  scarcely  an  exposure  being  free 
from  it.    Every  gradation  from  the  normal  type  to  the  pecu- 


5 


Fig  3.    Bedding  in  Orient  a  sandstone,  Amnicon  River,  Douglas  County. 

liar  features  described  above  can  be  found.  Usually  the  inclined 
layers  do  not  extend  through  more  than  a  few  feet  of  stratigra- 
phic  thickness,  but  some  long  gently  inclined  partings  may  rep- 
resent cross  bedding  developed  on  a  huge  scale.  At  some  places, 
where  the  waves  have  washed  off  a  large  terrace  along  the  shore, 
cross  bedding  may  be  seen  in  three  dimensions.  Then  the  in- 
clined layers  are  often  found  to  be  curved  into  sags,  domes,  and 
other  irregular  forms;  as  suggested,  many  down  curved  layers 
may  be  simply  cross  sections  of  this  kind  of  cross  bedding. 

The  dip  of  the  inclined  beds  is  often  rather  steep,  but  no  cross 
bedding  of  the  type  usually  ascribed  to  wind  action  was  observed. 
The  direction  of  dip  was  observed  with  some  care.  It  is  almost 
always  toward  a  northerly  or  easterly  direction.  In  the  Devils 
Island  sandstones  alone  are  southerly  or  southwesterly  dips  at 
all  common,  although  they  are  found  occasionally  in  all  the 
lower  strata.    The  significance  of  this  fact  is  the  presumption 


Wis.  Geol.  and  Nat.  Hist.  Survey. 


Bulletin  No.  XXV,  Plate  IV. 


A.  Down-curve  in  upper  beds  of  Orienta  sandstone,  west  side  of  Sand  Island, 
Bayfield  County. 


BAYFIELD  GROUP. 


31 


that  the  material  for  this  formation  was  brought  mainly  from 
the  northeast,  while  that  of  most  of  the  group  came  from  the 
opposite  direction. 

Iron  Banding.    In  noting  the  colors  of  the  Bayfield  group 
the  observer  is  often  confused  by  the  tendency  of  the  red  beds  to 
weather  white,  while  many  white  beds  are  discolored  to  a  brown 
shade  on  the  surface  or  are  stained  red  by  iron  from  overlaying 
rocks  or  drift.   Much  more  light  colored  sandstone  exists  than  is 
generally  supposed.   The  rapid  variations  of  color  are  often  very 
striking.   When  the  change  takes  place  along  a  joint  it  gives  the 
appearance  of  a  fault  which  is  often  very  deceptive.    In  general 
it  may  be  said,  that  the  coarse  grained  and  often  the  thick  bedded 
layers  are  lightest  in  tint,  while  the  thin  bedded  and  shaley  beds 
are  both  darkest  and  most  varied  in  color,  although  most  affected 
by  spots  and  streaks  of  lighter  tint.    Mottling  and  irregular 
blotching  of  red  and  white,  however,  is  not  confined  to  these 
beds.    When  this  kind  of  rock  is  seen  below  water,  where  the 
surfaces  are  cleaner  and  the  colors  brighter  than  where  exposed 
to  the  air,  the  effect  is  very  striking.    Sometimes  red  circles  are 
seen  in  white  sandstone,  inclosing  spots  of  white.    Often  very 
irregular  markings  occur.   Fine  banding  along  the  bedding  is  by 
far  the  most  common,  but  one  seldom  has  to  follow  the  bands  far 
before  they  leave  the  planes  of  deposition  to  form  irregular 
curves.    True  concretions  of  iron  oxide  are,  however,  not  very 
common. 

The  origin  of  these  varied  features  is  evidently  the  work  of 
ground  water,  but  the  reason  for  the  curious  forms  is  not  known. 
It  appears  probable  that  most  of  the  iron  was  originally  deposit- 
ed in  the  thin-bedded,  fine  grained  layers  and  in  the  massive 
brownstones,  and  that  it  has  spread  from  them  into  the  rest  of 
the  rock.  The  light  color  of  the  coarse  grained  sediments  sug- 
gests either  the  action  of  leaching  of  these  more  porous  beds,  or 
that  the  iron  was  never  deposited  in  them.  A  striking  instance 
of  secondary  coloration  was  observed  in  a  cross  bedded 
layer  near  Pikes  Quarry,  Bayfield  County,  in  which  the  upper 
half  was  red  and  the  lower  nearly  white,  the  line  of  junction 
thus  cutting  the  bedding.  Although  the  iron  oxide  is  not  an 
important  cement  in  the  firm  brownstone,  it  may  be  the  dom- 
inant cement  in  some  of  the  less  indurated  sandstones,  no  thin 


32 


BAYFIELD  GROUP. 


sections  of  which  have  been  examined.  The  writer  is  inclined 
to  believe  that  such  curious  forms  as  are  shown  in  Plate  I, 
B,  frontispiece,  are  due  to  partings  along  the  lines  of  iron  band- 
ing. Generally  these  apparent  folds  or  sharp  basins  occur  along 
joints,  thus  strengthening  the  suggestion  of  an  origin  due  to  ir- 
regular cementation,  although,  however,  all  are  not  to  be  ex- 
plained in  this  manner. 

Pebbles  and  Clay  Pockets.  In  a  formation  entirely  devoid 
of  fossils,  like  the  Bayfield  group  of  sandstones,  the  derivation 
of  the  pebbles  in  the  conglomerates  is  a  subject  of  considerable 
importance.  No  thick  beds  of  conglomerate  occur  within  the 
group,  but  pebbles  are  found  very  commonly  on  both  normal  and 
cross  bedding  planes  and  to  a  less  extent  scattered  through  the 
sandstone  or  even  through  the  shale.  The  Devils  Island  sand- 
stone, however,  is  free  from  them.  In  size  these  pebbles  average 
about  an  inch  in  diameter,  the  largest  being  some  four  inches 
across.  All  are  well  rounded.  By  far  the  greater  portion  of 
the  pebbles  are  porphyries  and  amygdaloids  with  some  basic 
traps;  these  were  obviously  derived  from  the  Middle  Kewcen- 
awan.  Next  follow  in  order  of  their  abundance,  vein  quartz,  red 
and  white  quartzite,  iron  formation,  chert,  slate,  and  granite, 
all  derived  from  the  Huronian  and  older  rocks.1  It  should  be 
noted  that  all  the  pebbles  with  the  exception  of  the  traps  are 
of  very  resistant  rocks,  while  even  those  are  the  hardest  parts 
of  the  formations  from  which  they  were  once  worn.  No  debris 
from  the  recognized  Keweenawan  sediments  (Oronto  group,  etc.) 
could  be  discovered. 

Often  associated  with  the  pebble  deposits  are  small  cavities 
which  when  seen  in  fresh  sandstone  are  found  to  contain  red  or 
green  clay.  Many  of  these  show  remnants  of  decomposed  trap 
pebbles  making  their  origin  at  once  evident.  Others  are  larger 
and  of  irregular  shape.  Yet  others  are  small  and  flattened,  ap- 
pearing at  first  sight  much  like  the  casts  of  shells.  But  again, 
in  fresh  rock  they  are  always  found  to  be  filled  with  clay.  A 
common  feature  of  clay  pockets  occuring  in  red  rock  is  a  sur- 
rounding rim  of  white. 


i  Owing  to  weathering,  the  identification  of  many  of  the  small  trap 
pebbles  is  quite  difficult. 


BAYFIELD  GROUP. 


33 


The  origin  of  the  irregular  or  flattened  clay  pockets  must 
•be  nodules  of  clay  laid  down  with  the  rock1.  Such  clay  lumps 
are  often  found  in  recent  deposits.  They  are  formed  of  flakes 
of  somewhat  indurated  clay  which  will  not  mix  with  sand,  or 
washed  out  by  streams,  or  dried  and  broken  up  by  sun  and 
wind  in  connection  with  mud  cracks.  Mud  cracks  are  not 
often  found  in  the  Bayfield  group  of  sandstones,  owing  to 
the  scarcity  of  clay  and  the  ease  with  which  they  are  over- 
looked in  natural  exposures. 

Chequamegon  Sandstone 

General  Character  and  Extent.  The  youngest  formation  of 
the  group  is  the  Chequamegon  sandstone,  so  named  from  the  ex- 
posures in  the  now  almost  idle  quarries  on  Houghton  Point  on 
Chequamegon  Bay,  Bayfield  County.  In  areal  distribution,  this 
formation  underlies  all  the  Apostle  Islands  southeast  of  a  line 
drawn  from  Sand  Point  to  Devils  Island.  How  far  it  extends 
beneath  the  thick  drift  of  the  Bayfield  Kidge  is  a  matter  of  con- 
jecture. The  Chequamegon  formation  consists  mainly  of  brown 
quartzose  sandstone. 

Thickness.  As  the  initial  dip  of  the  formation  could  hardly 
have  been  over  one  degree,  or  about  100  feet  per  mile,  and  thai 
presumably  towards  the  northeast  (cf.  p.  102)  we  may  compute 
a  thickness  of  nearly  two  thousand  feet;  but  in  order  to  allow 
for  the  probable  lessening  in  dip  towards  the  southeast,  as  well 
as  a  tendency  to  overestimate  the  degree  of  inclination,  a  thick- 
ness of  1000  feet  is  regarded  as  nearer  the  truth. 

General  Section.  The  Chequamegon  sandstone  may  be  di- 
wided  into  several  more  or  less  distinct  members  as  follows : 

Washburn  beds.  Soft  red  and  white  sandstones  with  much  band- 
ing and  mottling-  of  the  colors;  beds  usually  thin  with  few  peb- 
bles or  shale  layers,  which  sometimes  show  mud  cracks. 

Quarry  or  Brownstone  beds.  Heavily-bedded  dark  brown  ferru- 
ginous sandstone  with  pebbles  and  clay  pockets;  between  heavy 
beds  are  thin-bedded  layers  and  lenses  of  red,  micaceous  shale. 


i  The  writer  did  not  observe  any  evidences  of  decomposing  trap 
boulders.    Cf.  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  209. 

3 


34 


BAYFIELD  GROUP. 


Main  beds.  Much  the  same  as  the  brownstone  but  with  more  ir- 
regular bedding,  cross  bedding,  light  colored  and  coarse  pebbly 
sandstone,  and  red  shale  beds.  (It  may  be  that  the  quarry  rock, 
is  only  a  phase  of  this  division.) 

Basal  beds.  Thick,  cross-bedded  layers  of  white  or  brownish 
sandstone  with  pebbles;  lenses  of  red  and  yellow  thin-bedded 
rock;  some  ripple  marks. 

LOCAL  DETAILS. 

The  youngest  or  Washburn  beds  of  the  Chequamegon  sand- 
stone are  seen  in  the  shore  cliffs  south  of  Washburn  on  Che- 
quamegon Bay.  Here  are  exposures  up  to  nearly  40  feet  in 
height  of  soft  sandstone  of  all  colors.  There  are  many  rapid 
variations  from  white  to  the  darkest  red,  while  mottling  is  very 
common.  No  pebbles  were  observed.  The  beds  range  from  sev- 
eral feet  in  thickness  down  to  a  fraction  of  an  inch  in  the  dark: 
red  sandy  shale  beds. 

At  the  Barksdale  works  of  the  E.  I.  Du  Pont  Denemours  Pow- 
der Co.  a  well  shows  the  greatest  thickness  of  the  Chequamegon 
sandstone  known  at  one  locality.  It  is  clear  that  the  Devils* 
Island  sandstone  was  not  reached. 

LOG  OF  WELL  AT  BARKSDALE  POWDER  WORKS 

Drilled  in  190f>.  Situated  in  sec.  23,  T.  48,  R.  5  W.  at  elevation  of 
about  750  ft.  A.  T.    Samples  sent  by  courtesy  of  U.  S.  Geological  Sur- 


vey. 

Sample  No.  Thickness  Depth 

Pleistocene:  Feet  Feet 

1  Grayish-red,  sandy,  non-calcareous  clay   70 

2  Very  calcareous  reddish-gray  "hard-pan"  or 

sandy  cemented  till   20  90 

Chequamegon  sandstone: 

3  Soft   medium  grained   light   reddish  quartz 

sandstone   ■.   18 

4  The  same,  slightly  darker  and  harder   27 

5  Pinkish  white  coarser  and  subangular  grained 

quartz  sandstone    25 

6  Soft;  finer  grained  reddish  quartz  sandstone  20 

7  Soft,  very  coarse  gritty  or  conglomeritic  red 

sandstone  mixed  with  some  finer  sandstone  20  ; 


BAYFIELD  GROUP. 


35 


8  Soft,   nearly  pure  quartz  sandstone,  grains 

subangular  and  of  medium  size   30 

9  Sample  missing.    Said  to  be  same  as  last...  15 

10  Soft  fine  to  medium  grained  pinkish  quartz 

sandstone    15 

11  Much  the  same  as  the  last  but  with  somewhat 

more  rounded  grains    20 

12  Nearly  pure  white  sandstone,  otherwise  same 

as  last    20 

13  Sample  missing.    Said  to  be  soft  red  sandstone  45 

14  Sample  missing.    Said  to  be  white  conglom- 

erate with  much  water   30  375 

Depth  of  well    375  375 


At  the  quarry  just  north  of  the  city  very  similar  rock  is  seen, 
(see  Fig.  2,  p.  29).  Between  the  thicker  beds  occur  thin-bedded 
and  shaley  partings  which  sometimes  show  mud  cracks.  These 
exposures  show  a  dip  of  about  one  degree  to  the  south. 

Only  comparatively  small  exposures  occur  on  Madeline  Island, 
the  best  being  on  the  northernmost  point.  These  beds  show  a 
darker  color,  together  with  red  shaley  beds,  and  pebbly  layers. 
They  appear  to  be  a  portion  of  the  quarry  beds. 

The  now  virtually  idle  quarries  on  Houghton  Point  north  of 
Washburn  are  in  heavily-bedded  brownstone.1  Between  the 
heavy  layers  is  frequently  found  a  foot  or  more  of  thin-bedded  or 
softer  sandstone,  while  lenses  of  red  micaceous  shale  often  occur. 
At  other  places  the  bedding  planes  are  marked  by  coarse  yellowish 
grits  or  layers  of  pebbles.  Clay  pockets  also  occur.  Plate  III, 
A,  p.  26.  shows  a  thin  section  from  this  locality. 

Pike's  quarry  south  of  Salmo  shows  the  greatest  vertical  ex- 
tent of  the  formation  so  far  as  known  in  any  single  exposure. 
The  following  section,  from  top  down,  shows  the  downward  grada- 
tion of  the  quarry  beds  (numbers  7  to  9)  to  the  less  regularly 
bedded  and  variable  colored  layers  of  the  main  beds : 

i  Buckley,  E.  R.,  Building  and  Ornamental  Stones  of  Wisconsin, 
Wis.  Geol.  &  Nat.  Hist.  Surv.,  Bull.  IV,  1898,  pp.  187-192. 


36 


BAYFIELD  GROUP. 


SECTION  AT  PIKE'S  QUARKY,  SEC.  33,  T.  50,  R.  4  W. 

Thickness 


9  Weathered  and  broken  brownstone.   23  feet 

8  Tnin  bedded  and  cross  bedded  red  shaley  sandstone  with 

yellow  streaks  '.   6 

7  Heavily  bedded  brownstone  with  very  few  clay  pockets,  the 

best  quarry  rock   33 

6  Unexposed  below  level  of  railway  track   15 

5  Heavily  bedded  brownstone  in  lake  cliff,  the  top  much 

broken  up    35 

4  Thin  bedded,  red,  shaley  sandstone   8 

3  Heavy  layer  of  brownstone   8 

2  Gray  to  deep  red,  yellow,  and  white  sandstone,  varies  from 

shaley  to  pebbly  with  much  cross  bedding,  the  coarser 

phases  having  the  lighter  colors   12 

1  Heavily  bedded  coarse  pebbly  brown  sandstone   20 


Total  thickness,  about   150  feet 


Tm mediately  south  of  the  docks  at  Bayfield  is  a  good  exposure 
of  brown  sandstone  in  the  cliffs.  The  usual  thin  bedded  and 
sandy  shale  partings  occur  between  the  beds,  and  in  .  one  place 
is  found  a  small  lense  of  pure  clay  shale,  a  foot  or  two  in  thick- 
ness. This  is  of  varying  shades  from  deep  red  to  gray  and  green, 
and  grades  into  the  usual  sandy  shale;  the  associated  yellow 
sandstone  layers  are  also  seen. 

On  the  south  end  of  Basswood  Island  is  an  abandoned  quarry 
which  shows  about  25  feet  of  brownstone  in  heavy  layers.1  The 
bedding  planes  are  curved  both  up  and  down  from  the  normal. 
A  shale  layer  is  found  between  the  brownstone  beds  in  the  quarry 
and  the  same  material  is  said  to  have  been  reached  by  boring 
not  far  below  the  bottom  of  the  quarry.  Pebbles  and  clay  pock- 
ets are  abundant.  Plate  III,  B,  p.  26,  shows  a  thin  section  of 
this  rock. 

A  small  quarry  was  once  operated  on  the  northeast  corner  of 
Hermit  or  Wilson  Island.2  The  neighboring  shore  cliff  shows  thin 
bedded  and  cross  bedded  yellow  and  white  mottled  layers  be- 


1  Ibid.,  pp.  178-182. 

2  Ibid.,  p.  185. 


BAYFIELD  GROUP. 


37 


tween  the  heavy  beds  of  brownstone.  A  thin  section  shows 
fairly  well  rounded  grains  averaging  nearly  0.4  mm  in  diameter. 
About  a  fourth  is  altered  feldspar  including  much  microcline, 
although  orthoclase  is  predominant. 

Stockton  Island  shows  extensive  outcrops  on  its  eastern  end. 
There  the  waves  from  the  open  lake  have  worn  some  striking 
caves  and  deep  coves  along  the  joints.  The  sandstone  is  some- 
what redder  in  color  than  the  quarry  beds.  A  few  shaley  layers 
are  seen  but  most  of  the  bedding  is  heavy.  Some  long  partings 
dipping  gently  to  the  south  resemble  huge  cross  bedding,  but 
are  probably  inclined  joints.  Cross  bedding  is  common.  At 
the  southeastern  end  of  the  exposures  occurs  hard,  cross  bedded, 
white  sandstone.  Similar  rock  is  also  seen  on  Presque  Isle 
Point. 

Near  the  southwest  corner  of  Stockton  Island  is  a  large  aban- 
doned quarry  which  shows  a  thickness  of  73  feet  of  brownstone 
in  the  main  opening.1  Above  this  another  excavation  discloses 
rock  which  is  mottled  with  white.  The  upper  layers  all  show 
clay  pockets.  The  partings  are  often  shaley  and  show  cross 
bedding.  They  pinch  out  rapidly,  never  having  any  great  hor- 
izontal extent.  Sometimes  they  end  on  downward  pitches  of  the 
bedding,  but  in  other  places  the  layers  bend  up  and  are  cut  off 
by  the  heavy  layer  above  as  cross  bedded  layers  are. 

Outer  Island  exhibits  a  fine  exposure  along  almost  the  en- 
tire length  of  its  eastern  side.  The  sandstone  is  much  varied 
in  color,  ranging  from  the  usual  brownstone  to  pure  white. 
The  changes  are  very  rapid  and  often  take  place  along  joints. 
In  general  the  coarse  grained  cross  bedded  layers  are  lightest 
in  tint.  Plate  I.  B,  frontispiece,  represents  a  curve  in  the  bed- 
ding seen  near  the  southern  end  of  the  island ;  others  occur  but 
are  not  so  distinct. 

Some  interesting  exposures  occur  on  the  east  side  of  Oak  Is- 
land. At  the  northeastern  corner,  heavy  beds  of  brownstone 
with  interbedded  dark  shaley  layers  are  seen.  Coarse  yellow 
grits  also  occur.  Toward  the  south,  lenses  of  thin  bedded  yel- 
low and  white  banded  sandstone  appear,  and  also  some  hard 
white  and  brown  coarse  pebbly  layers. 

2  Ibid.,  p.  183. 


38 


BAYFIELD  GROUP. 


On  Point  Detour  and  the  adjacent  headlands1  occur  beds  of 
brown  sandstone  with  the  usual  shaley  partings.  The  depth 
to  which  weathering*  here  extends  is  unusual,  being  often  20 
feet  or  more. 

North  Twin  Island  shows  strata  near  the  bottom  of  the  Che- 
quamegon formation.  "White  to  brownish  heavy  cross  bedded 
layers  with  occasional  large  ripple  marks  occur. 

Bear  Island  shows  on  its  eastern  coast  a  very  good  section. 
The  southeasterly  dip  is  here  more  pronounced  than  it  is  to 
the  southeast,  so  that  some  400  feet  of  the  stratigraphic  thick- 
ness is  apparently  seen.  However,  the  layers  pinch  out  and 
vary  so  rapidly  that  an  exact  determination  is  impossible.  As 
we  go  north  we  descend  to  successively  older  and  older  strata. 
At  the  south,  brown  sandstone  with  irregular  cross  bedding  and 
lenses  of  thin  bedded  yellow  and  pink  sandstone  occur. 
But  towards  the  north  end  the  color  becomes  gradually  lighter 
until  hard  cross  bedded  white  beds  take  their  place.  These 
basal  beds  show  a  few  ripple  marks.  At  some  points  wide  ter- 
races of  rock  have  been  washed  clean  by  the  storms  so  that  an 
excellent  opportunity  is  given  to  study  the  curious  forms  of 
the  curved  cress  bedded  layers  (see  p.  30). 

On  York  Island,  at  the  northwestern  cape,  is  a  fine  exposure 
of  the  basal  layers  in  a  clean  wave-swept  terrace.  White  and 
reddish  sandstone,  with  grit  and  conglomerate,  occur  as  well  as 
small  lenses  of  thin  bedded  red  and  pink  layers. 

At  the  south  end  of  Devils  Island,  which  is  entirely  surrounded 
by  a  rock  cliff,  the  light  colored  basal  layers  of  the  Chequamegon 
sandstone  are  seen.  There  are  interbedded  layers  similar  to 
the  main  body  of  underlying  Devils  Island  sandstone,  so  that 
no  very  sharp  line  of  demarkation  can  be  drawn. 

Devils  Island  Sandstone. 

General  Character  and  Extent.  The  formation  of  the  Bay- 
field  group,  which  conformably  underlies  the  Chequamegon 
sandstone,  is  called  the  Devils  Island  standstone,  from  the  ex- 
cellent exposures  on  the  island  of  that  name.    It  is  distinguished 


i  Owen,  D.  D.,  Chippewa  Land  District,  p.  54;  Geol.  Survey  of  Wis., 
■etc.,  pp.  268,  305. 


BAYFIELD  GROUP. 


39 


from  the  other  formations  of  this  group  by  its  thin  bedding,  well 
rounded,  medium  sized  quartz  grains,  which  are  almost  free 
from  any  coating  of  iron  oxide,  by  ripple  marks,  and  by  its  pink 
and  white  color.  Banding  and  mottling  of  the  colors  is  frequent. 
A  few  iron  concretions  occur.  No  shale  beds,  feldspar  grains, 
clay  pockets  or  pebbles  are  known  in  this  formation.  The  form- 
ation is  much  more  porous  and  friable  than  the  others  of  the 
group.  For  that  reason  more  striking  and  larger  sea  caves  have 
been  wrorn  in  the  Devils  Island  sandstone  than  in  any  other  hor- 
izon. 

The  Devils  Island  sandstone  outcrops  along  a  narrow  belt 
stretching  for  twenty-five  miles  southwest  from  the  island  from 
which  it  takes  its  name.  Fine  exposures  occur  in  the  cliffs  of 
Sand  Island  and  Squaw  Bay  (Plates  V,  B,  XXIII,  A,  p.  94). 1 
Lesser  ones  are  seen  on  Siskowit  River  and  Lost  Creek  near 
Cornucopia.  Twenty-five  miles  to  the  southwest  an  isolated  ex- 
posure on  Brule  River  corresponds  so  closely  in  character,  that 
there  is  little  doubt  that  it  is  to  be  placed  in  this  formation. 
According  to  the  writer's  interpretation  of  the  structure  of  the 
district,  this  formation  must  lie  immediately  beneath  the  drift 
south  of  Washburn,  but  no  exposures  of  it  are  there  known. 
It  may  pinch  out  or  otherwise  disappear  in  the  interval. 

Thickness.  The  thickness  of  the  Devils  Island  sandstone 
cannot  be  directly  measured,  but  a  computation  based  upon  the 
width  of  outcrop  and  average  dip  places  the  figure  at  about 
300  feet. 

Ripple  Marks.  The  only  portion  of  the  Bavfield  group 
which  shows  ripplemarks  in  any  abundance,  is  the  Devils  Is- 
land sandstone  and  some  of  the  beds  immediately  above  and 
below.  The  accompanying  diagrams  show  the  most  common 
types.  Most  have  symmetrical  ridges,  little  if  any  sharper  than 
the  intervening  troughs.  The  other  type  has  one  side  of  the 
ridge  much  steeper  than  the  other,  as  shown  in  Fig.  4,  c,  and  Fig. 
5,  p.  40.  Few  were  observed  which  show  the  subordinate  ridge 
in  the  hollowT,  such  as  is  often  seen  in  modern  ripple  marks 
formed  on  the  lake  bottom  (Fig.  4,  b).    This  is,  however,  a 

i  Owen,  D.  D.,  Chippewa  Land  District,  p.  55;  Geol.  Survey  of  Wis., 
etc.,  p.  268. 


40 


BAYFIELD  GROUP. 


feature  which  is  readily  overlooked.  The  ripple  marks  occur 
both  on  cross  and  normal  bedding  planes,  and  where  marked  by 
a  cement  of  iron  along  the  bedding  the  effect  upon  the  outcrop 
is  very  striking  (Fig.  5).  In  size  they  average  one  to  two 
inches  from  crest  to  crest,  but  occasionally  much  larger  ones 
are  seen. 


A  B 


C  D 

Fig.  4.    Types  of  ripple  marks. 


It  is  believed  that  the  symmetrical  ripplemarks  are  the  result 
of  wave  action  in  standing  water;  and  that  the  unsymmetrical 
form  (Fig.  4,  c)  was  formed  by  currents,  either  of  water  or  air. 

Cr^ss  Bedding.  The  common  cross  bedding  of  the  Devils 
Island  formation  is  more  regular  than  much  of  that  in  the 
other  members  of  the  Bayfield  group.  The  curious  irregular 
curved  forms  there  noted  are  seldom  seen.    The  direction  of 


Fig.  5.    Ripple   marks   marked   by   iron  bandinjr  in    Devils   Island  sandstone 
(Specimen   li.058).    One-half  size. 

dip  of  the  layers  is  usually  to  the  south  or  southwest  but  there 
are  some  exceptions,  although  on  the  whole  it  is  conspicuous 
for  being  in  a  direction  opposite  to  that  prevailing  in  the  other 
formations.  This  fact  is  thought  to  mean  that  the  material  of 
the  Devils  Island  sandstone  was  brought  from  a  different  direc- 
tion. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey. 


Bulletin  No.  XXV,  Plate  V, 


B.  Sea  caves  in  Devils  Island  sandstone,  near  Squaw  Bay,  Bayfield  County 


BAYFIELD  GROUP. 


41 


O  R I E NT  A  S A NDSTO N  E 

General  Character  and  Extent.  Underlying  the  Devils  Is 
land  sandstone  occurs  the  lowest  formation  of  the  Bayfield  group, 
the  Orienta  sandstone,  so  called  from  its  exposure  in  the  quar- 
ries near  the  village  of  that  name.  In  its  upper  portion  this 
formation  resemhles  the  Chequamegon  sandstone  very  closely,  so 
that  the  possibility  of  repetition  of  that  formation  by  faulting 
was  considered.  It  is  seen,  however,  that  in  the  vicinity  of  Cor- 
nucopia tire  uppermost  beds  of  the  Orienta  pass  beneath  the 
Devils  Island  sandstone,  although  the  actual  contact  is  not  ex- 
posed so  far  as  known.  Moreover,  there  is  no  repetition,  so 
far  as  could  be  discovered,  of  the  Devils  Island  formation  to  the 
west.  In  its  lower  portion,  and  indeed  to  some  extent  through- 
out, the  Orienta  contains  more  feldspar,  mica  and  magnetite 
grains  than  the  younger  formations,  the  relative  amount  in- 
creasing towards  the  bottom,  as  do  beds  of  red  shale. 

The  Orienta  sandstone  underlies  the  Western  Plain,  extend- 
ing from  the  line  of  outcrop  of  the  Devils  Island  formation,  all 
along  the  south  coast  north  of  the  Douglas  Range  and  into  Min- 
nesota. Folding  brings  it  up  near  Ashland,  where  rock  be- 
lieved to  be  a  part  of  it  outcrops  on  the  South  Fork  of  Fish 
Creek,  and  it  is  found  beneath  the  thick  drift  in  deep  wells. 

Thickness.  As  with  the  Chequamegon,  there  is  no  direct 
means  of  measuring  the  thickness  of  the  Orienta  sandstone.  A 
computation  based  on  a  uniform  dip  of  but  one  degree  places  the 
thickness  on  Brule  River  at  about  1000  feet.  This  section  is 
not  good  enough  to  be  correlated  with  that  shown  on  Middle 
River,  where  the  formation  is  turned  up  by  the  thrust  fault  of 
the  Douglas  Range,  exposing  some  2,700  feet.  As  the  Devils  Is- 
land formation  does  not  occur  there,  it  appears  certain  that  the 
Middle  River  section  is  all  Orienta  sandstone,  thus  placing 
the  total  thickness  of  the  formation  at  3,000  to  3.500  feet;  2,495 
feet  of  this  formation  is  penetrated  by  the  deep  well  at  Ashland 
(see  p.  65),  and  1,110  feet  is  exposed  on  Fish  Creek. 

General  Section.  The  following  section  shows  the  subdivis- 
ions of  the  Orienta  sandstone  from  the  top  down.  In  the  future 
it  is  possible  that  some  parts  may  be  distinguished  as  separate 
formations : 


42 


BAYFIELD  GROUP. 


Approximate  Thickness 


Upper  beds.  Mainly  white  and  red  sandstone 
with  a  few  ripple  marks   300-400  feet 

Upper  brownstone  (of  Port  Wing)   500-700 

Copper  Creek  beds.  White  and  pink  fine  grained 
sandstone  with  magnetite  and  mica  grains  and 
a  few  ripple  marks   75-100 

Main  beds.  Brown,  red,  and  white  sandstones, 
becoming  progressively  more  felspathic  towards 
the  bottom,  with  thin  beds  of  red  shale   1800-2000 


Total  thickness,  about   2700-3200  feet 


LOCAL  DETAILS 

Aside  from  the  small  exposure  believed  to  belong  to  this  forma- 
tion, on  Fish  Creek  near  Ashland  Junction,  which  will  be  de- 
scribed in  Chapter  V,  the  easternmost  exposure  of  the  Orienta 
Sandstone  is  on  Sand  Island.  Here  and  on  Eagle  Island1  and 
Squaw  Point  (Plate  V,  A,  p.  40)  to  the  west,  occurs  white  cross- 
bedded,  ripple-marked  sandstone  much  resembling  the  basal  beds 
of  the  Chequamegon  formation.  A  few  layers  of  red  sandstone 
occur  and  there  is  much  banding  of  the  colors.  A  considerable 
amount  of  decomposed  feldspar  is  seen  among  the  sand  grains. 

To  the  west,  on  Siskowit  Point,  the  downward  gradation  of 
this  type  to  the  brownstone  beds  may  be  seen.  Lenses  of  red 
shale  also  appear  (Fig.  1,  p.  29).  A  small  quarry  formerly 
operated  here  produced  red  and  white  sandstone.  Similar  sand- 
stone with  red,  shaley,  and  yellow  gritty  layers  occurs  on  Bark 
Point,  across  a  bay  by  that  name  to  the  w^est. 

Just  west  of  the  little  settlement  at  Herbster  is  a  bold  rocky 
point  projecting  out  from  the  sandy  coast  cliffs.2  Here  the 
sandstone  is  pebbly  and  cross  bedded.  Plate  IV,  B,  p.  30,  shows 
an  interesting  trough  in  the  bedding  seen  here.  A  quarry  was 
once  started  at  this  locality. 

The  quarries  at  Port  Wing  are  still  operated  at  times  and 
produce  some  of  the  best  brownstone  in  the  region.  This  rock 
is  h'eavify  bedded,  free  from  clay  pockets,  has  few  pebbles,  and 


1  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  208. 

2  Owen,  D.  D.,  Geol.  Surv.  of  Wis.,  etc.,  1852,  p.  269. 


BAYFIELD  GROUP. 


43 


is  of  a  somewhat  redder  and  more  cheerful  tint  than  the  brown- 
stone  of  the  Chequamegon  sandstone.  In  the  quarry  some  peb- 
bles were  observed  along  the  bedding  planes,  together  with  black 
magnetitic  layers,  and  a  little  white  sandstone.1  Plate  VI,  A, 
p.  44,  shows  a  thin  section  of  this  rock.  About  a  fourth  is  feld- 
spar, mainly  orthoclase,  but  including  some  microcline  and  plagio- 
clase.  The  locality  is  notable  for  the  unusual  fact  that  the  rock 
is  sound  clear  up  to  the  top  and  shows  glacial  striae. 

Another  good  quarry  was  formerly  operated  on  the  east  bank 
of  Iron  River  near  Orienta,  in  the  western  part  of  Bayfield 
County.2  The  southeasterly  dip  of  the  formation,  combined 
with  the  fall  of  the  river,  brings  one  to  successively  higher  and 
higher  strata  in  ascending  the  stream.  "We  pass  from  the  heav- 
ily bedded  brownstone  up  to  thin  bedded  white  and  red  banded 
rock.  Near  the  road  crossing,  occur  white  and  yellow  heavier 
beds  with  thin  layers  of  green  shale.3 

West  of  the  mouth  of  Iron  River  no  exposures  occur  on  the 
'Coast.  Only  two  small  outcrops  occur  on  Brule  River  below 
those  of  the  Devils  Island  sandstone.  On  Poplar  River  are  good 
outcrops  for  several  miles  above  the  mouth,  but  as  the  dip  here 
is  generally  less,  no  great  thickness  can  be  observed.  The  rock 
is  thought  to  be  part  of  the  upper  brownstone.  Much  is  thin 
^bedded  and  grades  to  coarse  yellow  sandstone.  The  magnificent 
section  seen  on  Middle  River  shows  the  lower  portion  of  the 
formation  and  will  be  described  in  detail  in  Chapter  V. 

West  of  Middle  River,  exposures  are  much  less  satisfactory. 
'The  Copper  Creek  and  main  beds  are  the  only  ones  found.  On 
Amnicon  River  for  about  three-fourths  of  a  mile  below  the  falls, 
at  the  contact  with  the  trap,  occur  good  sandstone  exposures. 
The  dip  is  southeasterly,  except  close  to  the  trap,  and  some 
275  feet  of  beds  is  thus  exposed.  Of  these  the  lower  200  feet 
is  mainly  heavily-bedded  brownstone,  which  once  was  quarried  to 


1  Buckley,  E.  R.,  op.  cited,  pp.  201-205. 

2  Ibid.,  p.  209. 

s  Owing  to  bad  weather  the  survey  of  Iron  River  was  not  completed. 
No  exposures  were  seen  or  reported  where  we  would  expect  to  find  the 
'Devils  Island  sandstone  '.see  map).  Sweet,  E.  T.,  Geol.  of  Wis., 
vol.  Ill,  1873  9,  p.  322. 


44 


BAYFIELD  GROUP . 


a  considerable  depth.1  Associated  white  and  yellow  pebbly 
phases  and  magnetitic  bands  occur.  These  features  serve  to 
distinguish  the  beds  from  the  upper  brownstone  of  the  Port 
Wing  quarries,  although  the  possibility  of  lateral  change  in  the 
formation  must  be  taken  into  account.  Above  these  layers  oc- 
curs a  gradual  transition  to  the  Copper  Creek  beds.  These 
are  mainly  thin  bedded  pink  or  red  and  white  fine  grained  sand- 
stone. Much  cross  bedding,  sometimes  curiously  curved,  occurs 
(Fig.  3,  p.  30).  No  ripple  marks  were  observed,  and  this  fact, 
taken  in  connection  with  fine  grain,  magnetite  grains,  and  small 
thickness  lead  the  writer  to  regard  this  as  a  p  a  rt  of  the  Orienta 
sandstone  rather  than  a  lateral  change  in  the  Devils  Island  forma- 
tion. It  is  also  simpler  on  structural  grounds  to  assume  this 
correlation,  for  it  is  entirely  possible  that  these  beds  occur  un- 
der one  of  the  unexposed  intervals  in  the  Middle  River  section 
to  the  east. 

Similar  beds  appear  to  occur  at  two  small  exposures  which 
were  not  visited  by  the  writer.  One  of  these  is  in  Sec.  30,  T. 
48,  R.  10  W.  and  was  not  discovered  by  any  of  Prof.  Grant's 
party.2  Another  outcrop  in  Sec.  7,  T.  47,  R,  13  AY.,  was  exam- 
ined by  one  of  Prof.  Grant's  assistants  and  a  sample  preserved, 
which  shows  the  rock  to  be  very  like  that  at  the  falls  of  the 
Amnicon  River.    It  is  a  pebbly  reddish  and  white  sandstone. 

On  Copper  Creek  next  to  the  contact  with  the  traps,  a  small 
thickness  of  thin-bedded,  ripple-marked,  red  and  white  spotted 
sandstone  is  exposed,  which  in  many  respects  resembles  the  De- 
vils Island  sandstone.  It  is,  however,  much  darker  in  color  and 
is  therefore  thought  to  belong  to  the  same  horizon  as  the  rocks 
described  above. 

Farther  to  the  west,  below  the  lower  falls  of  Black  River  (Plate 
XIX,  p.  80)  occurs  red  and  white  spotted  irregularly  colored 
sandstone  varying  much  in  bedding  and  coarseness  of  grain.  The 
dip  may  be  sufficient  to  expose  as  much  as  200  feet  of  strata, 
showing  a  somewhat  similar  scccession  as  at  Amnicon  River 
(see  p.  43) .  No  true  brownstone  was  observed  and  there  is  a  com- 
parative abundance  of  magnetite,  micas,  and  ferromagnesian 

1  Buckley,  E.  R.,  op.  cited,  p.  208. 

2  Sweet,  E.  T.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  348. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey. 


Bulletin  No.  XXV,  Plate  VI. 


Photomicrographs  in  Ordinary  Light,  Magnified  12  Diameters.  (Buckley, 
Bull.  IV,  Plate  LXIV). 


A  ^ 


B 


A.  Orienta  sandstone  (specimen  4717)  from  Port  Wing.  The  section  shows 
more  feldspar  (mainly  orthoclase,  but  including  some  microcline  and  plagioclase), 
iron  oxide,  and  ferromagnesian  minerals,  than  those  from  the  Chequamegon  sand- 
stone, although  not  notably  different  from  Plate  III,  B,  p.  26.  The  cement  in 
this  specimen  is  partly  iron. 


B.  Orienta  sandstone  (specimen  4718)  from  quarry  on  St.  Louis  River,  in  bed 
1  of  section  on  p.  70.  Nearly  one-fourth  of  the  rock  is  feldspar,  mainly  ortho- 
clase, but  including  as  usual  some  microcline  and  plagioclase.  The  cement  is  in 
part  argillaceous,  being  composed  of  the  alteration  products  of  the  feldspars. 


BAYF1EFLD  GROUP. 


45 


minerals.  Ripple  marks  occur  but  rarely  and  cross  bedding  is  not 
very  abundant,  but  many  clay  pockets  and  pebbles  were  observed. 
Some  of  the  thicker  beds  are  of  yellowish  to  white  quartz  sand- 
stone. One  such  was  observed  to  fill  a  hollow  in  the  thin  bedded 
red  layers.  The  latter  type  of  rock  appears  to  be  more  abun- 
dant in  the  upper  part  of  the  section  but  often  occurs  as  lenses 
in  the  heavier  bedded  sandstones. 

In  Sec.  29,  T.  47,  R.  14  W.,  occur  several  small  exposures  of 
yellow  and  white  fine  grained  hard  sandstone,  very  much'  like 
some  of  the  beds  exposed  on  Copper  Creek.  A  well  at  Foxboro 
in  See.  6,  T.  46,  R.  15  W.,  almost  on  the  west  line  of  the  state, 
shows  the  same  kind  of  rock,1  as  do  some  small  exposures  near 
Holyoke  visited  by  Professor  Grout.2 

A  small  exposure  of  sandstone  is  said  to  exist  on  the  Nemadji 
River  in  the  NE14  Sec,  27,  T.  48,  R.  14  W.,  but  was  not  visited 
by  the  writer.3 

The  exposures  of  the  Orienta  sandstone  on  St.  Louis  River 
are  described  on  p.  69. 

Econamic  Products.  The  only  product  of  economic  value 
derived  from  the  Bayfield  group  is  building  stone.4  This  is 
obtained  from  the  most  ferruginous  phase  of  the  sandstone  which 
is  commpnly  known  as  "brownstone."  Apparently  this  rock 
is  found  only  in  certain  more  or  less  well  defined  horizons.  It 
will  be  noted  that  the  quarries,  especially  those  in  the  Apostle 
Islands^  are  arranged  in  a  nearly  straight  line  along  the  strike 
of  the  formation.  Therefore  but  one  horizon  of  good  quarry 
rock  is  believed  to  exist  in  the  Chequamegon  formation,  although 
good  stone  was  seen  at  many  scattered  points.  Less  is  known 
about  the  Orienta  sandstone.  The  best  brownstone  is  that  found 
at  Port  Wing  and  Orienta,  but  it  is  most  probable  that  the 
brownstone  quarry  on  Amnicon  River  is  at  a  lower  horizon. 


1  Drillings  sent  by  C.  N.  Edin,  Dedham,  Wis. 

2  Personal  communication. 

s  Sweet,  E.  T.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  318. 

4  A  full  description  of  the  quarries,  including  a  list  of  buildings, 
constructed  with  Lake  Superior  stone,  is  found  in  Bull.  IV,  Wis.  Geol.. 
and  Nat.  Hist.  Survey,  Building  and  Ornamental  Stones  of  Wisconsin,, 
by  E.  R.  Buckley,  1898,  pp.  167-219. 


46 


BAYFIELD  GROUP. 


The  quarry  at  Fond  du  Lac  does  not  produce  a  true  brownstone, 
the  rock  being  firmer,  more  felspathic,  and  irregularly  colored 
red  and  white. 

Condition  of  the  Quarry  business  in  1910.  When  the  writer 
visited  the  district,  no  quarry  happened  to  be  in  operation.  The 
Port  Wing  quarries,  which  alone  are  operated  on  an  extensive 
scale,  closed  down  about  the  first  of  July.  A  very  little  stone 
had  recently  been  quarried  at  Houghton.  The  Fond  du  Lac 
quarry  is  operated  whenever  the  height  of  water  in  the  river 
permits  shipments,  but  is  not  equipped  to  furnish  anything  but 
rubble  and  irregular  blocks. 

Causes  of  Decline.  The  causes  of  the  almost  complete  aban- 
donment of  this  once  apparently  flourishing  industry  do  not  lie 
wholly  in  the  character  of  the  stone  itself.1  A  few  decades  ago 
brownstone  was  a  very  popular  building  material  in  the  eastern 
part  of  this  country,  so  that  when  a  similar  stone  was  discovered 
in  Wisconsin  it  was  at  once  exploited.  Between  1868,  when  the 
first  quarry  was  opened  on  Basswood  Island,2  and  1893  the  bus- 
iness continued  to  grow.  A  few  years  before  1893,  a  boom  took 
place  at  the  head  of  the  lakes.  As  in  all  other  business  enter- 
prises, speculators  then  rushed  into  the  brownstone  industry. 
Stone,  often  of  inferior  quality,  was  put  out  at  ruinously  low 
prices.  The  bad  results  from  the  use  of  this  low  grade  material 
naturally  reflected  upon  the  reputation  of  the  good.  Then  came 
the  inevitable  panic,  resulting  from  the  unnatural  expansion  of 
business.  The  demand  for  stone  decreased  greatly  and  never 
again  reached  its  former  extent. 

>  In  the  meantime,  the  brownstone  buildings  of  the  east  had  be- 
gun to  look  shabby  and  a  cheerful  light  stone  was  demanded. 
This  was  supplied  by  the  Bedford  limestone,  which  is  nearer 
the  best  markets  and  possesses  the  great  advantage  of  softness. 
Tools  dull  much  more  rapidly  in  cutting  sandstone,  a  fact  wit- 
nessed by  the  extensive  blacksmith  shops  of  the  Lake  Superior 
-quarries.  Before  the  Lake  Superior  companies  could  recover 
from  the  results  of  their  folly  before  the  panic,  this  light  stone 
had  captured  the  market.    By  1897  very  little  stone  was  being 

1  Buckley,  E.  R.,  op.  cited,  p.  211. 

2  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,*  vol.  Ill,  p.  209. 


BAYFIELD  GROUP. 


47 


taken  out  and  today  only  two  quarries  are  producing  first  class 
building  stone.  Plants  representing  an  investment  between  two 
and  three  million  dollars  are  now  idle ;  some  have  been  burned  j 
in  most  the  machinery  is  rusted  and  useless  and  the  buildings 
are  falling  to  pieces.  At  several  quarries  large  piles  of  cut 
blocks  ready  to  ship  remain  unsold.1  Perhaps  now  that  business 
at  the  head  of  the  lakes  is  developing  upon  a  more  sane  and  whole- 
some basis  than  formerly,  quarrying  will  be  resumed;  for  the 
stone  has  a  useful  field  for  buildings  in  smoky  cities,  as  it  does 
not  show  dirt  like  the  lighter  toned  materials  now  in  fashion. 


i  In  1912  some  of  these  were  being  shipped. 


48 


OEONTO  GROUP. 


CHAPTER  IV 


THE  ORONTO  GROUP  AND  OLDER  FORMA 
TIONS,  AND  THE  EXTENSION  OF  THE 
SANDSTONE  GROUPS  IN  MINNESOTA 


Nomenclature.  Beneath  the  Bayfield  sandstone  group  de- 
scribed in  the  last  chapter,  is  a  great  thickness  of  arkose  sand- 
stone and  shales,  nearly  all  red  in  color,  and  for  the  most  part 
occupying  a  highly  tilted  position  wherever  exposed.  On  ac- 
count of  these  differences,  these  rocks  were  separated  by  the 
former  Geological  Survey  of  Wisconsin  from  the  overlying  hor- 
izontal quartzose  sandstone  (see  p.  16).  At  its  base  this  ark- 
ose group  is  interbedded  with*  the  traps,  thus  showing  that  it 
is  a  part  of  the  Keweenawan  series;  but  the  bottom  of  this  up- 
per division  of  the  series  is  assumed  to  be  the  base  of  a  thick 
conglomerate  called  the  Outer  Conglomerate,  above  which  hor- 
izon no  igneous  rocks  occur. 

With  the  exception  of  the  basal  portion,  this  group  has  not 
heretofore  been  divided  into  formations.  Professors  Lane  and 
Seaman  have  recently  applied  the  name  Freda  to  the  sandstone 
immediately  overlying  the  black  shale  beds  (Nonesuch  forma- 
tion) just  above  the  Outer  Conglomerate.1  As  this  formation 
(sometimes  known  as  the  WTestern  sandstone  of  Michigan]  is 
only  a  small  portion  of  the  entire  thickness  of  sediments  below 
the  Bayfield   group   which   have   not   yet   been    studied  in 


i  Lane,  A.  C,  and  Seaman,  A.  E.,  Geological  Section  of  Michigan, 
Rept.  of  State  Board  of  Geol.  Survey,  1908,  p.  23;  Jour,  of  Geology, 
vol.  15,  1907,  p.  36. 


ORONTO  GROUP. 


49 


detail,  it  seems  best  to  give  a  new  name  to  the  entire  group  and 
retain  the  name  Freda  for  this  formation.  It  will  therefore  be 
termed  the  Oronto  Group,  from  the  excellent  exposures  near 
the  bay  of  that  name  in  the  northern  portion  of  Iron  County. 
The  limits  of  the  group  may  be  fixed  at  the  bottom  of  the  Outer 
Conglomerate  as  a  base,  and  the  top  of  the  highest  thick  beds  of 
red  shales  and  well-marked  arkose  sandstones  as  the  top. 

General  Character.  The  Oronto  Group  is  composed  of  con- 
glomerate, sandstone,  and  shale;  the  last  probably  predomin- 
ating, although  not  often  exposed.  In  color  it  is  usually  some 
shade  of  red,  but  a  characteristic  feature  is  banding,  streaking, 
and  spotting  with  greenish  white.  The  white  beds  are  seldom 
more  than  a  few  inches  thick.  Often  the  light  color  also  extends 
along  the  joints.  In  the  material  of  the  component  grains  it 
differs  mainly  from  the  Bayfield  group  in  having  a  greater  pro- 
portion of  undecomposed  minerals,  feldspars,  micas,  and  ferro- 
magnesian  compounds,  as  well  as  more  mag^tite  and  calcium  car- 
bonate. Quartz  grains  are,  however,  present  in  considerable  quan- 
tity ;  but  are  never,  so  far  as  known,  predominant  throughout  any 
considerable  thickness  of  strata.  The  shale  is  usually  sandy  and 
micaceous,  but  there  are  considerable  beds  of  fine  clay  shale. 
Nearly  always  the  shale  beds  are  more  brightly  colored  than  the 
coarser  grained  strata, 

Areal  Extent.  In  areal  extent  the  Oronto  Group  underlies 
all  of  the  Eastern  Plain  (see  p.  12),  between  Ashland  and  the 
Southern  Trap  Highland,  but  it  is  exposed  at  but  few  points. 
It  is  probable  that  only  the  harder  beds  are  exposed,  since  these 
would  form  the  ridges  now  buried  beneath  the  drift,  which  is 
usually  so  thick  that  only  a  few  very  deep  wells  enter  the  rock. 
It  here  forms  a  series  of  open  folds  (see  p.  92).  Isolated  areas 
of  rocks  believed  to  belong  to  the  Oronto  Group  occur  also  on 
Middle  and  St.  Louis  rivers  in  Douglas  County,  and  rock  of  the 
same  type  is  penetrated  by  deep  wells  in  Superior.  The  Oronto 
Group  is  believed  to  extend  far  into  Minnesota,  for  rocks  of 
the  same  type  have  been  found  by  drilling  to  lie  beneath  the 
Paleozoic  sediments. 

Thickness.    The  thickness  of  the  Oronto  Group  can  only  be 
determined  by  computations  based  upon  discontinuous  exposures. 
The  sum  of  the  stratigraphic  thicknesses  actually  exposed  is 
4 


50 


OROXTO  GROUP. 


nearly  10,000  feet,  but  evidently  the  total  must  be  much  greater. 
On  Montreal  River  it  is  possible  that  a  thrust  fault,  dipping  to 
the  north,  might  cause  a  repetition;  but  no  direct  evidence  in- 
dicating its  existence  was  discovered.1  Computation  places  the 
thickness  of  the  Freda  sandstone  between  the  top  of  the  None- 
such shales  and  Lake  Superior  at  12,600  feet.  Should  an  in- 
itial dip  of  even  10  degrees  be  subtracted,  (which  is  much  too 
great),  the  result  would  be  11,700  feet.  On  Fish  Creek  to  the 
west,  where  there  is  every  probability  that  the  strata  are  thinner, 
since  they  thin  rapidly  in  that  direction  at  all  lower  horizons,2 
a  thickness  of  fully  8,000  feet  is  indicated.  There  the  jointing 
and  shearing  (see  p.  93)  do  not  indicate  that  the  thickness  is 
expanded  by  faulting.  Since  the  rocks  of  this  locality  are  be- 
lieved to  lie  at  a  horizon  above  those  of  Montreal  river,  a  total 
thickness  of  the  Oronto  Group  of  some  21,000  feet  is  indicated. 
This  figure  agrees  with  other  computations  based  upon  tire  dip, 
and  appears  to  be  conservative — provided  lateral  variations  in 
the  character  of  the  strata  along  the  strike,  and  concealed  fault- 
ing have  not  confused  the  true  sequence  to  a  greater  extent 
than  now  seems  probable. 

Subdivisions.  The  Oronto  Group  may  tentatively  be  sub- 
divided into  the  following  formations;  the  basis  of  the  division 
is  in  part  structural  but  is  mainly  lithologic,  and  therefore  rather 
unsatisfactory,  owing  to  the  possibility  of  lateral  variation  as 
mentioned  above : 

Thickness 

Amnicon  Formation.  Red  and  greenish  shales, 
arkose  sandstone,  and  some  conglomerate  (1050 
feet  exposed)    5,000  feet 

Eileen  Sandstone.    Red  and  white  somewhat  quartz- 

ose  sandstone  (1800  feet  exposed)   2.000 

Freda  Sandstone.  Fine-grained  red  and  greenish 
arkcse  sandstone  with  a  little  conglomerate  at  top 
and  bottom  (about  8000  feet  exposed)   12.000 


1  Lane,  A.  C,  and  Seaman,  A.  E„  Geol.  Section  of  Mich.,  Report  of 
State  Board  of  Geol.  Survey  of  Mich.,  1908,  pp.  33,  38. 

Personal  communications. 

2  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  12. 

  Copper  Bearing  Rocks,  Mon.  IT.  S.  G.  S.,  vol.  V,  pp.  153-230. 

n 


O  RON  TO  GROUP. 


51 


Nonesuch  Formation.    Black,  gray  and  red  arkppe 

and  shale  (maximum)   350 

Outer  Conglomerate,   coarse  conglomerate  (maxi- 

mum)    1.200 


Total  maximum  thickness,  about   21,550  feet 


Composition.  The  rocks  of  the  Oronto  Group  are  mainly 
composed  of  angular  to  subangular  fragments,  derived  from 
igneous  rocks  without  much  chemical  decomposition.  The  only 
marked  exceptions  are  some  of  the  red  clay  shales.  At  the  base 
in  the  Nonesuch  formation,  occur  many  layers  of  black  sand- 
stone composed  of  nearly  unaltered  fragments  of  trap,  so 
thoroughly  cemented  with  calcite  that  they  are  readily  mistaken 
for  igneous  rocks.  Higher  in  the  group  there  appears  a  greater 
proportion  of  debris  from  quartzose  rocks.  In  the  conglomer- 
ates there  is  little  difference  in  the  source  of  the  pebbles  from 
those  found  in  the  Bayfield  group.  They  comprise  traps  of 
many  varieties  (porphyries  probably  predominating),  quart- 
zite,  iron  formation,  chert,  vein  quartz,  slate,  and  granite.  In 
the  coarse  arkose  grits,  fragments  of  igneous  rocks  of  both  basic 
and  acid  varieties  are  plainly  seen,  but  these  rocks  were  not 
studied  in  detail.  In  most  of  the^roup  the  grain  is  so  fine  that 
the  microscope  is  needed  to  determine  the  material;  and  as  no 
detailed  study  was  made,  information  is  available  for  only  a  few 
varieties  of  rock.  This  will  be  found  under  the  head  of  local 
details,  page  54.  The  component  grains  are  mainly  feldspars 
(both  orthoclase  and  more  basic  varieties,  the  latter  being  often 
too  much  altered  to  determine),  quartz,  mica,  magnetite,  ferro- 
Tnagnesian  minerals  and  fragments  of  fine-grained  igneous  rocks. 
On  the  whole,  the  grains  are  less  rounded  than  those  of  the  Bay- 
field group  and  although  extremely  variable,  appear  to  average 
considerably  smaller  in  size.  Often  a  somewhat  clayey  reddish 
or  greenish  matrix  is  seen,  perhaps  derived  from  these  fine- 
grained porphyries,  from  the  decomposition  of  feldspar,  or  some- 
times mainly  composed  of  iron  oxide.  The  cement  is  often  caL 
cium  carbonate,  but  enlargements  of  the  feldspar  and  quartz 
grains  are  probably  the  dominant  cement.  Red  oxide  of  iron  is 
also  quite  abundant.  fa 


52 


ORONTO  GROUP. 


An  interesting  rock  which  was  examined  is  the  greenish  cal- 
careous sandy  shale  of  the  Amnicon  formation,  found  on  Middle 
River  (see  p.  66,  Plate  VII,  p.  50,  and  Plate  XVI,  A,  p.  72). 
In  the  thin  section,  calcium  carbonate  was  found  to  separate  the 
very  fine  angular  quartz  grains,  but  on  analysis  this  proved  to  be 
less  than  20%  of  the  rock.  These  ripple-marked  and  mud-crack- 
ed shales  are  interbedded  with  and  merge  into  red  noncalcareous 
shales  and  sandstone.  Red  spots  also  occur  within  the  greenish 
rock  and  greenish  within  the  red.  It  cannot  be  determined 
whether  or  not  the  calcium  carbonate  is  original  or  has  been 
introduced  into  the  rock  by  underground  waters  from  the  adja- 
cent traps. 

The  following  chemical  analyses  are  the  only  ones  available 
Tor  Wisconsin ;  unfortunately  they  mainly  represent  the  None- 
such formation,  which  is  wholly  composed  of  basic  debris;  none 
are  typical  of  the  great  body  of  the  group : 


ANALYSES  OF  SANDSTONE  OF  THE  OKONTO  GROUP.1* 
NONESUCH  FORMATION 


o' 

53 

O 
< 

• 

Q 

CaO 

O 
da 

s 

% 

rs 

s* 

ea 

o 

Total  J 

Locality. 
Bad  River  

54.50 
49.14 
55.91 
51.98 

Bad  River  

FREDA  SANDSTONE 


73.24 
68.91 

White  River  Falls  

AMNICON  FORMATION 


Bad  River  Falls  

69.78 
72.14 

15.4B 

7.93 

.49 

1.17 

2.64 

2.42 

99.86 

10.71 

.12 

8.55* 

*  Calculated. 


i  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  203.    Last  by  Victor  Lehner,  1911. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.       Bulletin  No.  XXV,  Plate  VIII. 

Eileen  Formation,  South  Fork  of  Fish'  Creek,  Sec.  19,  T.  47,  R.  5  YY.,  Town 
op  Eileen,  Bayfield  County. 


A.  Vertical  beds  of  red  and  white  streakel  feldspathic  sandstone,  showing 
horizontal  joints  (see  Plate  X,  B,  p.  56).    The  strike  is  nearly  east  and  west. 


B.  Vertical  beds  of  red  and  white  sandstone  and  sandy  red  shale.  Looking 
southwest. 


OR  ON  TO  GROUP. 


53 


Bedding.  The  bedding  of  the  Oronto  Group  varies  from 
shaley  to  layers  several  feet  in  thickness  (Plates  VII,  p.  50  ;  VIII, 
p.  52,  XI,  p.  58;  XVII,  A,  p.  74)  ;  but  in  general  it  is  thinner 
and  more  regular  than  that  of  the  Bayfield  sandstones.  How- 
ever, the  difference  may  in  part  be  accounted  for  by  the  fact 
that  the  exposures  of  this  group  are  smaller;  and  being  of  steep- 
ly-inclined layers,  they  expose  to  view  less  of  the  horizontal  var- 
iability of  the  beds.  A  very  striking  feature  of  much  of  the 
group  is  tire  extremely  rapid  variations  from  very  coarse  grit  or 
conglomerate  to  fine  shale.  Shale  is  very  often  interbedded  with 
conglomerate  through  a  considerable  thickness  of  strata,  the 
sharpness  of  contacts  and  scarcity  of  sandstone  being  remark- 
able (see  pp.  62,  106).  Cross-bedding  is  abundant,  but  us- 
ually small;  no  prevailing  direction  of  dip  was  discerned. 
Curved  beds  are  often  met  with,  some  being  shown  in  Figs.  6, 


lfoot 


Fig.  6.    Magnetite  sand  bed  in  Eileen  sandstone,  Fish  Creek,  Bayfield  County. 

and  7,  p.  55.  Channels  in  the  top  of  shale  beds,  filled  with 
sandstone,  are  very  common ;  an  example  is  given  in  Fig.  9,  p.  69. 
Ripple  marks  are  very  abundant,  being  mainly  of  the  symmet- 
rical type  and  rather  small  in  size  (see  Fig.  4,  p.  40).  These 
occur  in  the  finer  grained  rocks,  especially  shales,  the  surfaces 
being  often  greenish  or  red  shale,  or  decidedly  ferruginous  sand- 
stone. In  some  localities  mud  cracks  are  extremely  abundant; 
but  they  are  readily  overlooked,  for  they  do  not  show  on 
weathered  surfaces.  This  remark  also  applies  to  rain  prints, 
which  were  observed  at  but  one  point.  Frequently  none  of  these 
features  are  of  such  character  that  they  may  be  utilized  to  de- 
termine the  top  of  the  strata.  In  the  case  of  mud  cracks,  the 
filling  often  adheres  to  the  nearest  hard  sandy  layer,  whether 
it  is  above  or  below  the  original  surface.  When  developed  in 
typical  form,  cross-bedding  is  the  most  reliable  guide  to  the 
structure  (see  Fig.  8,  p.  63  and  Plate  XIc,  B,  p.  64).  Clay 
pockets  and  scattered  pebbles  are  not  common.  Most  of  the 
former  are  of  the  small  flattened  type  and  grade  into  small 
lenses  of  shale.    Veins  of  calcite  are  abundant. 


54 


ORONTO  GROUP. 


LOCAL  DETAILS 

Amnicon  Formation.  The  top  of  the  Amnicon  formation 
may  be  observed  on  Fish  Creek,  near  Ashland,  and  on  Middle 
and  St.  Louis  rivers  in  Douglas  County.  These  interesting  ex- 
posures and  their  correlation  will  be  described  in  the  succeeding 
chapter.  Aside  from  these  the  highest  known  beds  are  those  seen 
at  the  lower  falls  of  Bad  River,  in  sec.  25,  T.  47,  R.  3  W.  About 
750  feet  of  greenish  and  red  coarse  arkose  sandstone,  with  in- 
terbedded  red  shales,  are  there  exposed.1  Microscopic  examina- 
tion shows  that  the  rock  is  composed  mainly  of  small  fragments 
of  porphyry,  although  the  debris  of  basic  rocks  is  also  seen.  This 
is  confirmed  by  the  chemical  analysis  on  p.  52.  In  some  beds 
considerable  quartz  is  seen.  The  section  is  probably  near  the 
base  of  the  formation. 

Eileen  Sandstone.  In  sees.  20  and  21,  T.  47,  R,  5  W.,  Town 
of  Eileen,  Bayfield  County,  the  valley  of  the  South  Fork  of 
Fish  Creek  exposes  about  1800  feet  of  sandstone  in  vertical  beds. 
The  bedding  varies  from  heavy  to  shaley  with  a  little  clay  shale 
as  shown  in  plate  VIII,  p.  52.  The  colors  range  from  brick  red, 
or  occasionally  even  deeper  shades,  to  clear  white  and  show  much 
mottling  and  banding  of  red  and  white.  Beds  composed  almost 
exclusively  of  magnetite  are  also  seen.  Some  are  as  much  as 
eighteen  inches  in  thickness  but  have  only  a  slight  lateral  extent. 
Ripple  marks,  cross-bedded  and  irregularly  bedded  or  domed 
beds  occur,  as  shown  in  Figs.  6  and  7.  Pebbles  are  not  very  com- 
mon. Microscopic  examination  (Plate  X,  B,  p.  56)  shows  that 
only  a  third  of  the  rock  is  quartz.  Feldspars  (mainly  ortho- 
clase  with  some  microcline  and  plagioclase,  more  or  less  altered), 
magnetite,  mica,  iron  oxides,  and  rarely  altered  ferromagnesian 
minerals  make  up  the  larger  portion  of  the  rock.  Trie  grams 
are  decidedly  angular,  as  is  usual  in  all  the  sandstones  of  the 
region.    Were  it  not  for  the  structural  relations,  however  (see 

i  Trving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  pp.  14,  202;  Copper- 
Bearing  Rocks,  Mon.  U.  S.  G.  S.,  vol.  V,  p.  132.  Irving  states  that  2000 
feet  of  strata  were  then  seen,  but  the  writer  was  able  to  find  but  the 
one  exposure,  about  three-eighths  of  a  mile  long.  No  map  of  the  river 
is  accurate. 


O  RON  TO  GROUP. 


55 


section,  p.  63,  and  structure  sections  on  map)  these  rocks 
might  be  regarded  as  tire  lower  part  of  the  Orienta  formation. 

On  the  west  side  of  Clinton  (locally  known  as  Marble,  or" 
sometimes  Graveyard)  Point,  are  low  ledges  dipping  at  a  moder- 
ate angle  to  the  northwest,  exposing  some  1,300  feet  of  fine- 
grained and  somewhat  shaley  to  heavily  bedded  sandstone 
(Plate  IX,  p.  54).  In  general  character,  it  most  resembles  the 
last  described  beds  and  so  is  correlated  with  them.  It  is,  how- 
ever, not  greatly  different  from  the  rocks  exposed  on  Bad 
River  (see  p.  54).    Ripple  marks,  cross-bedding  and  contorted 


,4  feet 

Fig.  7.    Bedding  in  Eileen  sandstone,  Fish  Creek,  Bayfield  County. 

bedding,  as  well  as  indistinct  mud  cracks  are  observed.  A 
thin  section  (Plate  X,  A,  p.  56)  from'  a  representative  phase 
shows  not  over  a  quarter  of  the  rock  to  be  quartz;  the  re- 
mainder is  feldspar,  about  half  orthoclase  and  half  plagioclase, 
as  well  as  ferromagnesian  minerals  and  micas.1  The  minerals 
show  considerable  secondary  enlargement.  The  cement  is  quartz, 
feldspar,  and  calcite.  These  rocks  were  formerly  correlated  erro- 
neously with  the  Bayfield  Group  (see  pp.  15,  18). 

At  Mason,  in  eastern  Bayfield  County,  the  well  at  the  mill  of 
the  White  River  Lumber  Co.  penetrates,  beneath  145  feet  of  drift, 
650  feet  of  sandstone  with  occasional  beds  of  red  sandy  shale, 
presumably  belonging  to  the  Eileen  formation. 

Freda  Sandstone.  Below  the  dam  across  White  River,  in 
sec.  6,  T.  46,  R.  4  W.,  is  an  exposure  of  some  300  feet  of  strata, 
as  shown  in  Plate  XI,  B,  p.  58.  This  rock  consists  of  coarse,  red 
and  greenish  arkose  alternating  in  rather  thin  beds,  with  red 


i  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  pp.  16,  209.  Copper- 
Bearing  Rocks,  Mon.  U.  S.  G.  S.,  vol.  V,  p.  366. 

Lane,  A.  C,  and  Seaman,  A.  E.,  Geol.  Section  of  Michigan,  Report 
State  Board  of  Geol  Survey  of  Mich.,  1908,  p.  33. 


56 


ORONTO  GROUP. 


and  green  micaceous  shales.  Some  poorly  developed  ripple 
marks  and  mud  cracks  were  observed.  Lithologically,  this  sec- 
tion might  be  assigned  either  to  the  horizon  of  the  Bad  Eiver 
rocks,  or  to  the  top  of  the  Amnicon  formation,  as  seen  on  Fish 
Creek  five  miles  to  the  north  (see  p.  62)  •  but  on  structural 
grounds  (see  section  E-P  on  general  map)  it  is  simpler  to  as- 
sume that  it  lies  at  the  top  of  the  Ffeda  sandstone,  in  the  gap 
between  the  Oronto  Bay  and  Fish  Creek  sections  (see  p.  50) 1 

In  the  valleys  of  the  streams  that  flow  into  Oronto  Bay,  in 
Iron  County,  occur  numerous  excellent  exposures  of  the  Freda 
sandstone  (Plate  XI,  A,  p.  58).  The  prevailing  rock  is  red,  fine 
grained  arkose.  Some  thin  greenish  beds  occur.  There  are  also 
numerous  beds,  usually  rather  thin,  of  markedly  micaceous  red 
shale.  Toward  the  base  of  the  formation,  the  grain  becomes 
coarser,  and  there  is  found  a  100-foot  layer  of  conglomerate. 
The  exposures  represent  a  thickness  of  over  12,000  feet,  but 
they  are  separated  into  two  groups,  with  an  unexposed  interval 
of  some  4,000  to  5,000  feet  of  stratigraphic  thickness.  As  as- 
sumed in  the  case  of  the  other  interval  of  no  outcrops,  it  is  most 
probable  that  the  lack  of  exposures  is  due  to  the  softness  of 
the  rock  (see  p.  21).  Microscopic  examination2  shows  that  less 
than  a  fourth  of  the  rock  is  quartz,  the  bulk  being  feldspars  and 
fragments  of  porphyries  and  basic  eruptives  with  reddish  de- 
composition products,  micas,  ferromagnesian  minerals,  and  mag- 
netite. The  cement  is  usually  red  oxide  of  iron,3  but  in  some 
cases  it  is  calcium  carbonate,  and  to  some  extent  quartz.  The 
quartzes  and  feldspars  show  secondary  enlargements. 

The  Freda  sandstone  is  also  exposed  on  Potato  Kiver,  within 
the  area  of  the  map,  but  this  locality  was  not  visited  by  the 
writer.4 

Nonesuch  Formation.  Exposures  of  the  Nonesuch  forma- 
tion of  the  Oronto  group  occur  on  the  Montreal,  Oronto.  ami 


1  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  pp.  14,  202. 

2  Irving,  R.  D.,  and  Chamberlin,  T.  C,  Observations  on  the  Junction 
between  the  Eastern  Sandstone  and  the  Keweenaw  series  on  Keweenaw 
Point,  Lake  Superior,  IT  S.  G.  S.  Bull.  23,  1885,  p.  82. 

s  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  pp.  12,  199.  Copper 
"Bearing  Rocks,  Mon.  IT.  S.  G.  S.,  Vol.  V,  pp.  133,  226. 

4  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  pp.  188,  202. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.  Bulletin  No.  XXV,  Plate  X. 

Photomicrographs  in  Ordinary  Light,  Magnified  12  Diameters. 


A.  Fine-grained  arkose  sandstone  from  Clinton  Point,  Iron  County  (specimen 
11.124).  The  grains  run  from  .1  to  .3  mm.  in  diameter.  About  25  per  cent 
are  quartz.  The  remainder  is  about  half  orthoclase,  the'  other  half  being  micro- 
cline,  plagioclase,  ferromagnesian  minerals,  mica,  and  iron  oxide.  Calcite  is  in 
some  places  seen  forming  a  cement.  Most  of  the  cementation  is,  however,  due 
to  enlargements  of  the  quartz  and  feldspar  grains.  This  section  should  be 
compared  with  those  of  the  Bayfield  group  shown  in  Plates  III,  p.  26,  and  VI, 
p.  44,  the'  rock  having  formerly  been  placed  in  that  group. 


B.  Medium-grained  red  sandstone  from  Eileen  formation  on  South  Fork  of 
Fish  Creek,  Bayfield  County  (specimen  11,369).  This  rock  differs  mainly  from 
A,  in  the  size  of  grains,  which  average  nearly  .3  mm.  About  a  third  of  the 
rock  is  quartz,  the  remainder  being  mainly  orthoclase.  Some  plagiioclase, 
micas,  and  ferromagnesian  minerals  are  found.  The  large'  white  areas  are  holes 
in  the  section. 


ORONTO  GROUP. 


57 


Potato  rivers.  This  member  is  composed  of  red,  gray  and  black 
arkose  and  shale,  often  with  calcareous  cement.  Microscopic  ex- 
amination shows  that  the  rocks  are  composed  of  virtually  un- 
altered debris  of  basic  eruptives.  The  thickness  on  Montreal 
River  is  about  350  feet,  lessening  rapidly  to  the  west.1 

Outer  Conglomerate.  Beneath  the  Nonesuch  shale  is  round 
the  great  Outer  Conglomerate,  which  is  1,200  feet  thick  on  Mon- 
treal River,  but  thins  to  only  800  feet  on  the  Potato.  On  the 
former  stream,  it  outcrops  in  magnificent  cliffs  over  200  feet  in 
height.  The  conglomerate  is  composed  of  pebbles  averaging 
four  or  five  inches  in  diameter — some  measure  fifteen  inches 
or  more.  They  are  from  the  diabase,  porphyry,  gabbro, 
and  other  rocks  of  the  Middle  Keweenawan  series,  with  subordin- 
ate, amounts  of  Huronian  quartzite,  iron  formation,  slate,  and 
chert,  as  well  as  granite  and  vein  quartz,  probably  derived 
mainly  from  the  Archean.  There  is  practically  no  matrix  of 
sand,  and  the  bedding  is  only  apparent  where  there  are  thin 
layers  of  coarse  arkose  sandstone.  As  in  the  higher  beds,  cal- 
eite  veins  are  common. - 

OLDER  FORMATIONS 

The  Traps.  Beneath  the  base  of  the  Outer  Conglomerate  is 
found  a  great  series  of  interbedded  traps,  conglomerate,  sand- 
stone, and  shale.  This  reaches  a  thickness  of  some  1,200  feet  on 
the  Montreal,  but  to  the  southwest  thins  out  to  nothing  within 
a  few  miles.  Below  this  occur  the  traps  of  the  Middle  Keween- 
awan, including  both  extrusive  and  intrusive  rocks.  These 
rocks  also  occur  in  the  Douglas  Range.3 

The  Pre-Keweenawan  Recks.  Still  farther  to  the  southeast, 
the  Huronian  sediments  are  found  in  a  position  stratigraphically 
below  the  eastern  traps;  and  then  in  turn  the  older  Archean 
granites,  schists,  and  greenstones  (see  p.  7). 

1  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  200.  Copper  Bearing 
Rocks,  Mon.  U.  S.  G.  S.,  vol.  V,  1883, 'pp.  133-226. 

2  Irving,  R.  D.,  Geol.  of  Wis.,  1873  9,  vol.  Ill,  pp.  12,  202. 

s  In  S.  E.  %  of  N.  E.  \i  sec.  19,  T.  47,  R.  4  W.,  near  Ashland,  a  huge 
mass  of  trap  6u  feet  across  rises  from  the  clay  plain.  As  no  rock  is 
found  in  neighboring  wells,  the  writer  believes  that  this  is  simply  an 
enormous  boulder,  and  not  an  outcrop  as  believed  by  some. 


58 


ORONTO  GROUP. 


Economic  Products.  So  tar  as  known,  no  products  of  econ- 
omic value  are  found  in  the  Orcnto  group.  In  contrast  to  the 
earlier  sedimentary  series  of  the  Lake  Superior  region,  it  con- 
tains no  iron  formation.  Thin  lenses  of  nearly  pure  magnetite 
occur  in  places,  especially  along  Fish  Creek ;  but  they  are  hardly 
greater  in  amount  than  the  magnetitic  sands  of  the  modern 
lake  beaches,  or  the  drift.  Most  of  the  rock,  with  the  possible 
exception  of  parts  of  the  Eileen  sandstone  on  Fish  Creek  is 
entirely  unsuited  for  building  stone.  Occasionally,  however, 
some  of  the  red  shale  has  been  used  for  paint  rock.  Traces  of 
copper  and  silver  have  been  found  in  the  Nonesuch  formation,1 
but  no  concentration  of  these  minerals  or  the  abundant  ferric 
oxide  is  known  to  have  taken  place  in  Wisconsin. 

The  rocks  of  the  Oronto  group  carry  little  water  and  such 
little  as  is  found  is  often  salty  (see  pp.  66,  73,  102). 

The  Extension  of  the  Sandstone  Groups  into  Minnesota. 
The  Bayfield  and  underlying  Oronto  groups  of  sandstones  ex- 
tend  into  Minnesota,  as  shown  by  Hall2,  between  the  continua- 
tion of  the  Douglas  Trap  Range  to  the  southeast  and  the  Huron- 
ian  and  Archean  rocks  to  the  northwest.  The  drift  is  so  thick 
along  this  narrow  strip,  however,  that  the  actual  continuity 
with  the  Paleozoic  sediments  to  the  south  is  somewhat  doubtful.3 
Nevertheless,  a  brief  discussion  of  this  question  is  not  out  of 
place. 

Most  of  the.  rock  exposed  in  this  belt  is  a  weli  indurated, 
rather  fine  to  medium  grained,  quartz  sandstone  pinkish  to  yel- 
low or  gray  in  color.  This,  the  rock  of  the  well  known  quarries 
of  the  Kettle  River  region,  is  much  like  the  sandstones  found 
near  the  falls  of  Black  River  in  Douglas  County4  (see  p.  4.1  . 


1  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  206. 

2  Hall,  C.  W.,  Keweenawan  Area  of  Eastern  Minn.,  Bull.  Geol.  Soc 
America,  vol.  XII,  1908.  p.  313. 

3  Grout,  F.  F.,  personal  communications. 

4  Grout,  F.  F.,  personal  communications. 
Weidman,  S.,  personal  communications. 

It  may  not  be  too  great  a  stretch  of  the  imagination  to  suggest  that 
these  light  colored  rocks  may  be  equivalent  to  the  Devils  Island  sand- 
stone of  the  Apostle  Islands. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.  Bulletin  No.  XXV,  Plate  XI. 


A.  Red  and  greenish  arkose  sandstone  and  shale  of  Freda  sandstone,  on  east 
bank  at  mouth  of  Oronto  River,  Iron  County. 


B.  Red  and  green  shale  and  arkose  grit  of  Freda  formation,  below  dam  of 
White  River  electric  plant.  Sec.  6,  T.  46.  R.  4  W.,  Ashland  County.  The  north- 
easterly strike'  is  plainly  indicated  by  the  outcropping  ridges  ;  the  dip  is  25  de- 
grees to  the  southeast,  away  from  the  observer. 


ORONTO  GROUP. 


59 


Still  farther  to  the  south  and  southeast,  in  the  valley  of  the 
St.  Croix  River,  appear  flat-lying,  yellowish  or  pinkish  quartz 
sandstones,  bearing  fossils  of  Upper  Cambrian  age.  These  rocks 
(the  Potsdam  sandstone  of  Wisconsin)  rest  with  pronounced  un- 
conformity upon  both  the  tilted  traps  of  Keweenawan  age  and  the 
older  Pre-Cambrian  rocks.  The  known  Cambrian  rocks  are 
separated  from  those  of  the  Kettle  River  district  by  a  consider- 
able drift-covered  interval,  probably  underlain  largely  by  trap 
and  granite,  as  wTell  as  by  the  great  fault  of  the  Douglas  Range 
which  is  known  to  extend  far  into  Minnesota,  forming  the  north- 
western border  of  the  traps.1 

In  many  places  deep  drilling  has  shown  that  the  Potsdam 
rests  upon  a  great  thickness  of  red  clastic  rocks.  These  red 
rocks  fill  a  great  depression  in  the  surface  of  the  Pre-Cambrian 
crystalline  rocks.2  The  thickness  of  these  red  rocks  varies  from 
nearly  2,500  feet  in  the  center  of  the  basin  down  to  nothing  at 
both  sides  of  the  trough  and  to  the  south,  where  the  Potsdam 
rests  directly  upon  the  Pre-Cambrian  igneous  and  metamorphic 
rocks.  But  few  wells  have  penetrated  the  entire  thickness  of 
the  red  clastic  series  near  the  center  of  the  basin.  At  Minne- 
apolis they  are  found  to  rest  upon  granitic  rock,  while  at  Still- 
water, apparently  at  the  center  of  the  trough,  Keweenawan  dia- 
base lies  beneath  (see  p.  60). 

The  red  series  is  studied  with  difficulty  as  it  is  not  known  to 
reach  the  surface.  The  only  information  is  derived  from  churn 
drill  records  and  is  hence  rather  unsatisfactory.  N.  H.  Win- 
chell3  believed  they  were  a  conformable  connection  of  the  Cam- 
brian with  the  Keweenawan'.  More  recently  C.  W.  Hall  re- 
studied  the  question,  reaching  the  same  conclusion  (see  p.  20), 4 

"Phe  red  clastic  series  consists  of  red  shale  and  sandstone  while 
some  fragmental  volcanic  rocks  are  thought  to  exist.    The  sand" 


1  Hall,  C.  W.,  Keweenawan  Area  of  Eastern  Minn.,  Bull.  Geol.  Soc. 
America,  vol.  XII,  1901,  p.  313. 

2  Hall,  C.  W.,  Meinzer,  O.  E.  and  Fuller,  M.  L.,  Geology  and  Under- 
ground Waters  of  Southern  Minnesota,  U.  S.  G.  S.  Water  Supply  Paper 
256,  1911,  pp.  32,  48. 

s  Winchell,  N.  H.,  Geol.  of  Minn.,  vol.  I,  1882,  pp.  422,  424,  537. 
4  Hall,  C.  W.,  The  Red  Sandstone  Series  of  S.  E.  Minn.  Unpublished 
manuscript  not  available.    Abstract,  Science,  vol.  27,  1908,  p.  722. 


60  ORONTO  GROUP. 

stone  is  mainly  composed  of  quartz  grains,  but  much  of  it  con- 
tains more  or  less  feldspar  and  is  very  frequently  calcareous. 
It  is  not  always  red,  for  occasionally  white  sand  is  reported. 

The  following  record  of  the  well  at  Stillwater  gives  a  good 
idea  of  the  lithologic  character  of  the  series : 

LOG  OF  STILL  WELL  DEEP  WELT  1 

Pleistocene  Thickness 

Glacial  drift    18  feet  • 

Cambrian 

Mendota  limestone    85 

Potsdam  sandstone;  calcareous  sandstone  of  gray  to 

yellowish  color  and  some  gray  shale   592 

Upper  Eeweenawan 

Dark  red,  sandy  calcareous  shale   13 

Coarse  quartz  sandstone   5 

Fine  dark  red  calcareous  shale   11 

Fine  dark  red  calcareous  sandstone  with  some 

calcite  and  pink  feldspar  grains   2233  2262 

Middle  Eeweenawan 

Diabase    450 

Depth- of  Well    3447  feet 

In  general,  these  rocks  are  exactly  like  those  of  the  Upper 
Keweenawan  series  of  the  Lake  Superior  basin,  whose  continu- 
ation they  must  be ;  while  beyond  doubt  the  basin  in  which  they 
lie  is  part  of  the  Lake  Superior  syncline  which  passes  up  Che- 
quamegon  Bay.  and  thence  southeasterly  across  Wisconsin  (see 
p.  88) .  The  portion  in  southeastern  Minnesota  is  probably  every- 
where separated  by  the  traps  of  the  north  side  of  the  basin,  from 
the  belt  northwest  of  the  fault  in  which  lies  the  lighter  colored 


i  Hall,  C.  W.,  Meinzer,  0.  E.  and  Fuller,  M.  L.,  Geology  and  Under- 
ground Waters  of  Southern  Minnesota,  IT.  S.  G.  S.  Water  Supply 
Paper  256,  1911,  p.  366. 

Meads,  A.  D.,  The  Stillwater  Deep  Weil.  Bull.  Minn.  Acad.  Nat.  Sci., 
vol.  Ill,  No,  2,  1891,  pp.  274-7. 

Winchell,  N.  H.,  Natural  Gas  in  Minnesota.  Minn.  Geol.  and  Nat. 
Hist.  Survey,  Bull.  V,  1889,  p.  25. 


ORONTO  GROUP. 


61 


sandstones  of  the  Kettle  River  region.  A  connection  west 
of  the  fault,  through  the  heavily  drift-covered  region  of  Anoka 
County,  Minnesota",  is  nevertheless  possible. 

Whether  or  not  these  buried  red  rocks  are  conformable  be- 
neath the  Upper  Cambrian  marine  sediments  is  a  question  be- 
yond the  scope  of  the  present  report.  On  the  whole,  the  ocur- 
rence  of  the  red  series  in  a  basin,  overlapped  on  both  sides  by 
the  overlying  horizontal  sediments  which  rest  with  pronounced 
unconformity  upon  the  tilted  Keweenawan  traps,  favors  the  view 
that  an  unconformity  also  exists  between  the  sandstones  (see 
p.  103).  Such  an  unconformity  probably  could  not  be  recognized 
in  the  records  of  churn  drill  holes. 


62  RELATION  OF  SANDSTONES. 


CHAPTER  V 


THE  RELATION  OF  THE  BAYFIELD  AND 
OROXTO  SANDSTONE  GROUPS 


General  Statement.  The  study  of  the  relation  of  the  Oronto 
and  Bayfield  groups  of  sandstones  was  the  principal  object  of 
the  present  investigation.  Outcrops  are  so  scarce  that  we  can 
at  no  place  trace  the  two  sandstone  groups  to  a  point  of  contact 
where  their  relations  may  be  absolutely  determined.  But  it  is 
possible  to  find  exposures  at  points  where  we  should  expect  to 
to  find  the  contact  of  the  Bayfield  and  Oronto  groups. 
At  all  of  these  localities  there  is  a  conformable  gradation  from 
quartz  sandstone  of  the  general  type  of  the  Bayfield  group 
downward  into  red  shales,  and  arkose  sandstone  or  conglom- 
erate of  the  same  general  type  as  the  main  body  of  the  Oronto 
group.  Sections  showing  this  general  stratigraphic  succession 
are  found  on  the  south  fork  of  Fish  Creek,  near  Ashland,  not 
far  from  the  main  area  of  the  Oronto  group,  in  the  deep  well  at 
Ashland,  on  Middle  and  St.  Louis  rivers  in  Douglas  County,  and 
in  deep  wells  in  Superior.  This  widespread  stratigraphic  se- 
quence shows  a  gradation  between  the  two  general  types  of  sand- 
stone formations  and  is  believed  to  indicate  that  the  Bayfield 
and  Oronto  groups  are  conformable. 

Fish  Creek.  Beginning  at  the  east,  there  is  found  an  expos- 
ure of  the  supposed  base  of  the  Bayfield  group,  in  the  town  of 
Eileen,  near  Ashland  Junction,  in  eastern  Bayfield  County.  Here 
the  valley  of  the  South  Fork  of  Fish  Creek  exposes  rock  in  sec- 
tions 11,  14,  and  15.  T.  47,  R.  5  W.  These  exposures  have  never 
been  described  previous  to  the  present  study.    The  beds  are  ver- 


Wisconsin  Geol.  and  Nat.  Hist.  Survey. 


Bulletin  No.  XXV,  Plate  XIa. 


RELATION  OF  SAXDSTOXES.  63 

tieal  or  inclined  steeply  to  the  north,  decreasing  from  90°  at  the 
south  to  70°  at  the  north  end  <  f  the  section,  while  the  strike  is 
approximately  east  and  west  (sec  p.  93)..  (See  Plates  XI  b,  p.  62, 
and  XI  c,  p.  64).    The  following  section  is  based  upon  a  chained 


Fig.  8.     Diagram    showing   the  use  of    cross-bedding,    in    determining  top  of 
vertical  strata.    The  top  is  to  the  right. 

plane  table  survey  made  by  the  writer  in  1912,  as  shown  in  Plate 
XI  a.  The  thickness  are  therefore  accurate.  Although  the 
exposures  are  not  continuous,  the  rock  is  everywhere  so  near  the 
surface  that  abundant  fragments  permit  the  general  character 
of  the  strata  to  be  determined. 

SECTION  ON  SOUTH  FORK  OF  FISH  CHEEK,  BAYFIELD  COUNTY 

Bayfield  Group:    Orienta  Sandstone.  Thickness 

Feet. 

14.  Heavy  to  thin-bedded  medium  grained  brown  quartz 
sandstone,  often  cross  bedded.  This  rock  is  of  the 
typical  Bayfield  type,  being  apparently  nearly  all 
quartz,  but  with  some  mica  flakes  and  feldspar 
grains.    Is  pebbly  in  places      .....  50 

13.  Red  and  white  spotted,  thin  to  medium  bedded  and 
cross  bedded  quartzose  sandstone.  A  thin  section 
(Plate  XII,  p.  66)  shows  that  three  quarters  of 
the  rock  is  quartz,  the  remainder  being  mainly 
orthoclase   .  .        .        .        .        .       .  75 

12.  Unexposed,  but  shows  abundant  fragments  of  red  grit 

and  coarse  red  and  white  sandstone       .        .        .  150 

11.  Red  grit  in  small  ledge    ......  5 

10.  Unexposed,  but  shows  fragments  as  before       .       .  65 


64 


RELATION  OF  SANDSTONES. 


9.  Red  grit  in  place       ........  5 

8.  Unexposed,  but  shows  fragments  as  before       .       .  130 
7.  Red  grit  and  red  and  white  sandstone       ...  10 
6.  Unexposed,  but  shows  fragments  as  before       .       .  190 
5.  Medium  to  heavily  bedded  coarse  brownish  red  and 
white  (often  in  spots)  sandstone  with  red  and  green- 
ish shaley  partings  and  some  red  grit.    A  thin  section 
from  the  coarse  sandstone,  with  minute  layers  and 
pockets  of  shale,  shows  that  it  is  not  greatly  differ- 
ent from  the  higher  strata.    Mc'st  of  the  feldspar  is 
orthoclase  but  some  microline,  plagioclase,  and  mica 
are  seen.  Most  of  the  section  (Specimen  11401)  is  red 
shale  composed  of  hue  grains  of  quartz  cemented  by 
iron  oxide  and  the  decomposition  products  of  feld- 
spars, etc.    A  thin  section  (Plate  XII,  B)  from  the 
coarse  white  sandstone  shows  that  less  than  half  the 
rock  is  quartz.    The  grains  are  angular  and  vary 
from  2.  mm  to  below  .25  mm  in  diameter.    Mica  is 
abundant   .        .        .        .        .        •        •  •  230 

4.  Unexposed,  but  shows  fragments  of  rock  like  the  last  100 
3.  Thin  to  medium  bedded  shaley  to  gritty  red  and  white 

sandstone         ........  15 

2.  Unexposed,  but  shows  fragments  like  the  adjacent 

rocks  •       •  .     •  85 


(Oronto  Group:    Amnicon  Formation. 

1.  Coarse  red  and  white  spotted  arkose  grit.  Conglom- 
erate with  pebbles  seldom  over  3  inches  in  diameter 
of  trap,  vein  quartz,  quartzite,  slate,  iron  formation, 
and  chert.  The  beds  vary  from  a  foot  to  15  feet  in 
thickness  with  subordinate  layers  of  coarse  arkose 
sandstone  and  red  and  greenish  shales.  There  is 
some  cross  bedding  (see  Plates  Xlb,  XIc)        .        .  1,050 


Total  thickness 


2,160 


An  unexposed  interval  of  nearly  5.000  feet  separates  this  sec- 
tion from  the  outcrop  of  the  Eileen  sandstone  in  Sees.  20  and  21. 

This  section  is  quite  important,  since  it  throws  new  light  on 
the  structural  relations  of  the  sandstone  groups.  It  is  but  five 
miles  from  the  area  of  rocks  undoubtedly  belonging  to  the  Or- 
onto group.  The  lowermost  beds  of  this  section  are  as  highly 
tilted  as  any  of  the  recognzied  Oronto  group,  and  match  it  ex- 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.  Bulletin  No.  XXV,  Plate  Xlb. 


A.  General  view,  looking  southeast,  on  South  Fork  of  Fish  Greek,  XE  y±  of 
NE  V±,  Sec.  15,  T.  47,  R.  5  W.,  Bayfield  County.  The  rocks  are  red  conglom- 
erate and  grit,  with  some  red  shale,  and  are  correlated  with  the  Amnicon 
formation.  The  dip  is  to  the  north  and  varies  from  70°  to  9-0°,  while  the 
strike  averages  N.  85°  W. 


B  Exposures  upstream  from  A,  looking  east.  The  rocks  are  the  same,  hut 
with  more  layers  of  red  shale. 


RELATION  OF  SANDSTONES. 


bo 


actly  in  lithologic  character.  The  anticline  of  which  they  form 
part  of  the  north  limb  involves  at  least  8,000  feet  of  strata. 
This  fold  must  belong  to  the  general  system  of  Keweenawan  folds 
(see  p.  95),  since  there  is  no  known  subsequent  period  of  de- 
formation with  which  it  could  be  correlated.  The  correlation 
of  the  lower  horizons  of  the  Fish  Creek  section  with  the  Oronto 
group  seems  therefore  to  be  very  well  established. 

The  correlation  of  the  upper  quartzose  beds  with  the  Bayfield 
group  is  much  less  definite.  A  drift-covered  interval  of  about 
three  and  one-half  miles  exists  between  the  most  northerly  ex- 
posure on  Fish  Creek  and  the  outcrops  of  the  Chequamegon 
sandstone  on  Wayman  Point.  This  belt  was  carefully  explored 
but  no  exposures  could  be  discovered,  and  the  inhabitants  of 
the  region  unite  in  saying  that  none  exist.  The  evidence  on 
which  the  upper  layers  are  correlated  with  the  base  of  the 
Orienta  sandstone  depends  on  three  factors: 

1.  The  lithologic  likeness  is  complete  and  can  be  better  appre- 
ciated in  the  field  than  in  a  description.  The  bedding  is  also 
characteristic  of  the  upper  group,  being  frequently  very  heavy, 
but  giving  way  rapidly  to  thin  cross-bedded  layers. 

2.  The  dip  of  the  beds  decreases  towards  the  north  end  of 
the  section,  thus  indicating  a  probable  flattening  out  of  the  beds 
to  the  north  (see  structure  section  E-F,  on  map). 

3.  The  deep  well  at  Ashland  encounters  a  very  similar  suc- 
cession of  beds  to  that  shown  in  the  section  on  Fish  Creek,  and 
indicates  a  pronounced  flattening  of  the  beds  to  the  north. 

Ashland  Well.  At  the  plant  of  the  Lake  Superior  Iron  and 
€hemical  Company  in  Ashland  three  miles  to  the  northeast  of 
Fish  Creek,  is  a  well  3,095  feet  in  depth.  Although  not  situated 
in  direct  line  between  the  most  northerly  exposure  on  Fish  Creek 
and  the  nearest  exposures  on  the  northwest  shore  of  Chequam- 
egon Bay,  nevertheless  if  the  position  of  the  well  is  projected 
parallel  to  the  probable  strike  of  the  rocks,  it  will  be  found  to 
occupy  a  position  well  to  the  north  of  the  Fish  Creek  exposures, 
thus  serving  very  well  to  fill  in  the  unexposed  interval.  If  the 
red  shales  there  encountered  represent  even  approximately  the 
horizon  of  those  seen  on  Fish  Creek,  from  which  they  differ  only 
in  lacking  the  conglomerate  beds,  a  flattening  out  of  the  beds 
5 

< 


66 


RELATION  OF  SANDSTONES. 


toward  the  north  is  indicated  (see  structure  section  E-F).  While 
it  cannot  be  positively  stated  that  any  of  the  beds  encountered 
in  the  well  belong  to  the  Bayfield  group,  it  is  nevertheless  shown 
that  the  usual  stratigraphic  succession  of  sandstone  grading 
down  into  red  shales  is  here  found. 

LOG  OF  "JUMBO"  WELL  AT  ASHLAND 

Drilled  in  1889  at  works  of  Lake  Superior  Iron  and  Chemical  Com- 
pany, near  west  y±  post  of  Sec.  5,  T.  47,  R.  4  W.  Elevation  of  curb^ 
660  ft.  A.  T.  Record  from  original  log,  furnished  by  Mr.  J.  E.  John- 
son, Jr.,  manager,  1910. 

Thickness  Depth 

Pleistocene:  Feet  Feet 

Red  clay      .       .  .       .       .       .  40 

Till  with  boulders  43 

Red    sand  92  175 

Bayfield  Group:    Orienta  Sandstone. 

Principally  fine  grainod  sandstone  of  red  color 
with  few  white  IWs,  and  bands  of  red  shale 
from  one  to  ten  *^et  thick.  A  soft  stratum 
30  feet  thick  feet  from  the  top,  fur- 

nishes most  ol  the  water.  The  flow  did  not 
increase  below  it.    The  water  is  said  to  be 

salty   2,495  2,670 

Oron'o  Group ;    Amnicon  Formation. 

Red    shale   425  3,905 

Depth  of  well   3,095  3,095 

Middle  River.  On  Middle  River,  in  eastern  Douglas  County,  m 
occurs  perhaps  the  most  interesting  exposure  in  the  entire  dis- 
trict. Here  over  3.000  feet  of  strata  are  exposed  in  a  great  over- 
turned fold.  The  structure  of  the  locality  is  shown  in  Plate 
XIII,  p.  66,  which  is  based  on  a  paced  survey  made  by  Grant  in 
1899.1  (See  also  Plate  VII,  p.  50;  Plate  XVII,  B.  p.  74;  and 
Plate  XXI,  90). 

i  Grant,  U.  S.,  Copper-Bearing  Rocks  of  Douglas  County,  Wis.  Geol. 
and  Nat.  Hist.,  Survey,  Bull.  VI,  1900,  pp.  18,  20. 
Personal  communications. 

Sweet,  E.  T.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  347. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey. 


Bulletin  No.  XXV,  Plate  XII. 


Photomicrographs  in  Ordinary  Light,  Magnified  12  Diameters. 


A.  Medium-grained  feldspathic  sandstone  (specimen  11,404),  from  South  Fork 
of  Fish  Creek,  Sec.  11,  T.  47,  R.  5  W.,  Bayfield  County.  Average  diameter  of 
grains  .35  mm.  Seventy  per  cent  of  the  rock  is  quartz,  the  remainder  being 
feldspars  (mainly  orthoclase,  but  some  microcline)  and  iron  oxide.  The  cement 
is  quartz.  It  should  be  noted  that  the  rock  does  not  differ  greatly  from  those 
of  the  Bayfield  group,  Plates  III,  p.  26,  and  VI.  p.  44. 


B.  Coarse-grained  white  arkose  sandstone  (specimen  11,397),  from  a  lower 
horizon  than  A.  The  average  size  of  the  grains  is  .5  mm,  but  the  largest  (of 
microcline)  is  2.0  mm.  long.  Quartz  makes  up  half  of  the  rock  ;  the  remainder 
is  mainly  orthoclase,  but  there  is  much  plagioclase :  little  iron  oxide  is  present. 
The  coarseness  and  angularity  of  the  grains,  as  well  as  the  greater  proportion 
of  feldspar,  should  be  compared  with  A. 


RELATION  OF  SANDSTONES. 


67 


SECTION  ON  MIDDLE  RIVER,  DOUGLAS  COUNTY 

Thickness 

Orienta  Sandstone.  Feet 
12.  Horizontal  thick-bedded  light  pinkish  brown  sand- 
stone; grains  are  of  medium  size  and  appear  to  be 
mainly  quartz.    The  oanding  with  red  and  white 
(see  p.  31)  often  gives  the  impression  of  folds. 
Estimated  thickness         ......  225 

11.  Unexposed,  but  showing  fragments  of  thick-bedded 

brown  sandstone      .        .        .  .  .  100 

10.  Thin-bedded   reddish   sandstone  apparently  contain- 
ing a  larger  proportion  of  feldspar.    Dips  35°  N.  50 
9.  Coarse  white  sandstone  with  pebbles  of  trap  and 
quartz;    some   is   very   calcareous    (Spec.  11243) 

Dips  60°  N  .        .  50 

8  Unexposed,  probably  contains  the  Copper  Creek  beds  300 
7.  Medium  to  coarse  grained  pebbly,  brown  sandstone; 
beds  very  heavy  and  hard  to  make  out,  but  appear 
to  be  vertical    Shows  iron  banding.    It  may  cor- 
respond to  the  brownstone  of  Amnicon  River  (see 
p.  43).    Grains  of  feldspar  and  mica  are  apparent 
to  the  unaided  eye.    Under  the  microscope  (Speci- 
men 11240),  it  is  seen  that  these  constitute  not  over 
a  quarter  of  the  rock,  the  remainder  being  quartz. 
Micrccline  and  plagioclase  are  distinguishable,  al- 
though most  of  the  feldspar  is  orthoclase.  Biotite 
is  also  seen      .        ...       .        .        .  .  250 

6.  Unexposed  ........  200 

5.  Fine  grained  red  sandstone,  apparently  containing 
more  feldspar  and  mica  than  higher  beds;  coarse, 
soft,  brown  sandstone;  reddish,  medium-grained, 
more  feldspathic  sandstone  in  vertical  beds.  The 
coarser  rock  was  examined  microscopically  (Plate 
XIV,  A,  p.  68)  and  found  to  be  over  two-thirds 
quartz.  The  subangular  grains  average  .35  mm. 
diameter.  Some  large  microcline  fragments  were 
discovered.  It  is  not  notably  different  from  the 
brownstone  at  Port  Wing  (see  p.  42  and  Plate 
VI,  A,  p.  44).  The  cement  is  alteration  products 
derived  from  the  feldspars       .....  250. 


68 


RELATION  OF  SANDSTONES. 


4.  Medium  to  fine-grained  pinkish  or  brownish  sandstone 
with  frequent  greenish  bands  and  spots.  Pebbles 
and  clay  pockets  are  not  common.  Some  beds  are 
cross-bedded  or  show  curious  curved  forms;  most 
are  in  heavy  layers  making  the  stratification  diffi- 
cult to  determine  (see  Plates  XVII,  B,  p.  74  and 
XXI,  p.  90).  Towards  the  base  a  few  thin  layers 
of  red  shale  occur.  Two  thin  sections  from  the  top 
and  bottom  of  the  horizon  were  examined  (Speci- 
mens 11233  and  11235).  The  grains  average  less 
than  .3  mm.  in  diameter  and  are  slightly  more 
angular  than  in  higher  strata.  Quartz  constitutes 
from  a  third  to  a  half  of  the  material.  The  re- 
mainder is  almost  whblly  much  altered  feldspar, 
mainly  orthoclase.  Occasionally  microcline  is  seen, 
as  well  as  a  few  altered  ferromagnesian  minerals 
and  mica.  The  cement  appears  to  be  quartz  and 
feldspar  enlargements,  with  some  iron  oxide    .        .  1,000 

3.  Red  shale,  dips  about  70°  S  10 

2.  Fine-grained  thin-bedded  hard  red  and  greenish  gray 
spotted  sandstone.  Dip  varies  from  45°  S.  to  80°  S. 
Under  the  microscope  this  is  seen  to  be  little  differ- 
ent from  the  lower  part  of  the  bed  above  (Plate 
XIV,  B,  opposite).  Less  than  half  is  quartz.  The 
grains  average  about  .25  mm.  diameter  and  are  ce- 
mented by  quartz  and  feldspar.  Microcline  and 
plagiocla.rs  may  be  distinguished  in  the  feldspars 
but  most  of  them  are  much  altered,  generally  to 
kaolin.  Ferromagnesian  minerals  and  mica  can  also 
be  seen    .       .       .       .       .       .       .       .       .  275 


Total  thickness  of  Orienta  sandstone      ....  2,735 

Amnieon  Formation. 

1.  Purplish  red  and  light-greenish-gray  very  fine-grained 
sandstone  to  sandy  shale,  in  beds  seldom  over  an 
inch  thick.  Dip  varies  from  60°  S.  to  vertical. 
Ripple  marks  and  mud  cracks  are  decidedly  abund- 
ant. There  is  scarcely  any  cross  bedding.  In  but 
one  place  were  found  ripple  marks  by  which  the 
inversion  of  the  strata  could  be  demonstrated!  (see 

i  Most  of  the  ripple  marks  are  of  the  symetrical  indeterminate  type^ 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.       Bulletin  No.  XXV,  Plate  XIV. 
Photomicrographs  in  Ordinary  Light,  Magnified  12  Diameters. 


A.  Coarse  friable  brownstone'  (specimen  11,236)  from  bed  5.  Middle  River, 
Douglas  County.  Tbe  grains  are  fairly  well  rounded  as  compared  witb  tbe 
older  sandstones,  and  average  about  .35  mm.  in  diameter.  The'  rock  is  over 
two-thirds  quarts.  The  remainder  is,  as  usual,  feldspar,  in  which  some  large 
microcline  fragments  are  conspicuous.  The  cement  is  composed  of  alteration 
products  from  the  feldspars. 


B.  Pine-grained  pink  feldspathic  sandstone  (specimen  11,232)  from  bed  2. 
The  grains  are  somewhat  more  angular  than  in  A.  and  average  .25  mm.  in 
diameter.  Less  than  half  of  the  rock  is  quartz.  Most  of  the  feldspar  is  ortho- 
clase,  but  microcline  and  plagioclase  are  also  abundant.  Ferromagnesian  min- 
erals, including  micas,  also  occur.  The  cement  is  quartz  and  feldspar,  stained 
with  iron.  This  section  should  be  compared  with  A,  as  well  as  with  Plates  X, 
p.  56,  and  XII,  B,  p.  66. 


RELATION  OF  SANDSTONES. 


p.  90).  A  thin  section  (Plate  XVI,  A,  p.  72) 
from  one  of  the  greenish  layers  was  examined.  It 
consists  of  extremely  fine  angular  grains  of  quartz 
(diameter  about  .01  mm.),  with  a  few  feldspars,  im- 
bedded in  a  matrix  of  crystalline  calcite  which 
forms  over  a  third  of  the  slide,  but  analysis  shows 
that  it  is  less  than  20%  of  the  total  (see  p.  52). 
Mica  flakes  are  seen  in  places,  being  concentrated 
on  some  bedding  planes.  The  red  noncalcareous 
phase  was  not  examined  microscopically       .        .  365 


Total  thickness  3,100 

In  the  field  the  lithological  likeness  of  the  lower  beds  of  this 
section  to  the  upper  part  of  the  known  Amnicon  formation  of 
the  Oronto  group  is  more  striking  than  any  description  can 
make  it,  so  that  the  writer  has  no  reasonable  doubt  of  the  cor- 
relation as  given.  However,  it  must  be  remembered  that  the 
distance  from  undoubted  outcrops  of  the  Oronto  group  is  con- 
siderable. 

St.  Louis  River.  At  the  extreme  northwest  corner  of  the 
state,  on  St.  Louis  River,  and  extending  for  a  short  distance 
into  Minnesota,  is  an  exposure  of  about  730  feet  of  conglomer- 
ate, sandstone,  and  shale.  These  beds  are  prevailingly  red  in 
color  but  are  spotted  and  streaked  with  white  or  greenish-gray. 
They  contain  much  feldspar,  decreasing  in  amount  towards  the 
top  of  the  section  (Plates  VI,  B,  p.  44,  and  XVI,  B,  p.  72).  Rip- 
ple marks,  mud  cracks,  and  rain  prints  are  abundant  (Fig.9). 


5  feet 


Fig.  9.    Redding   in   Amnicon  formation,   St.   Louis  River,  Minn. 

In  all  their  characters  they  are  like  the  upper  part  of  the 
Oronto  group,  and  insensibly  grade  upward  into  rock  like  that  of 
the  lower  part  of  the  Orienta  sandstone. 


70 


RELATION  OF  SANDSTONES. 


The  following  detailed  section  is  based  upon  one  given  by  N. 
H.  Winchell  of  the  Minnesota  Survey,  supplemented  by  the  ob- 
servations of  the  writer.1  The  dip  varies  from  3°  to  10°  to  the 
southeast  (see  Plate  XV,  opposite). 

"Winchell  was  inclined  to  assume  the  existence  of  an  uncon- 
formity between  the  lowest  conglomerate,  which  is  mainly  com- 
posed of  pebbles  of  vein  quartz,  and  that  which  overlies  it  and 
is  composed  of  basic  trap  pebbles.  He  found  a  pebble  in  the 
latter  which  he  supposed  to  have  been  derived  from  the  pyritif- 
erous  quartz  conglomerate.  The  writer  found  no  evidence  for 
such  a  division.  A  large  pebble  of  Keweenawan  porphyry  (Spe- 
cimen 11272)  was  found  in  the  lower  conglomerate,  and  there  is 
a  complete  gradation  between  the  two  types  (see  p.  17). 

SECTION  ON  ST.  LOUIS  RIVER  FROM  FOND  DU  LAC  TO  THE  POWER  HOUSE 

Thickness 

Or'enta  Sand  stone.  Feet 

1.  Upper  Sandstone  Beds.    Reddish  brown  sandstone  of 

medium  grain  (about  .4  mm.)  spotted  with  and 
grading  into  white.  Contains  pebbly  bands,  and 
micaceous  shaley  layers.  The  pebbles  are  trap, 
vein  quartz,  and  quartzite.  The  bedding  varies 
from  thick  to  thin  and  cross-bedded.  The  quarries 
are  on  this  bed.  Under  the  microscope,  the  grains 
are  seen  to  be  subangular.  About  tivo-tJiirds  of  the 
rock  is  quartz,  the  remainder  being  more  or  less  al- 
tered feldspar,  mainly  orthoclase  (see  Plate  VI,  B, 
p.  44).  Microcline,  plagioclase,  mica,  magnetite, 
and  various  ferromagnesian  minerals  appear.  Specks 
of  red  iron  oxide  also  appear,  but  the  cement  is 
quartz  200 

2.  Dark  red  shale,  with  greenish  layers  and  spots    .        .  18 

3.  Lower  Sandstone  Beds.    Sandstone  much  like  1.  Is 

somewhat  finer  grained  and  contains  more  mica, 
shaley  beds,  red  and  green  clay  pockets,  and  beds 


i  Winchell,  N.  H.,  Amer.  Geol.,  vol.  16,  1895,  pp.  75,  150;  Minn.  Geol. 
&  Nat.  Hist.  Survey,  10th  Ann.  Kept.,  1881,  pp.  30,  91;  Id.,  23rd  Ann. 
Report,  1894,  p.  239;  Geology  of  Minn.,  1899,  vol.  IV,  p.  15. 


RELATION  OF  SANDSTONES. 


71 


of  magnetitic  rock.  Under  the  microscope  (Speci- 
men 11328)  shows  little  difference  from  1,  except  that 
not  much  over  half  is  quartz  and  there  is  more  mica  70 


Total    Orienta    sandstone       ......  288 

Amnicon  Formation. 

4.  Red  shale,  like  2  10 

5.  Alternating  beds  of  sandstone  and  red  shale.  Thick- 

ness not  accurately  known.  Under  the  microscope 
(Specimen  11326)  shows  medium-sized  (about  .3  mm. 
diameter)  grains;  all  are  subangular.  Not  much 
over  half  arc  quartz,  the  remainder  being  mainly 
altered  feldspars  of  all  kinds,  orthoclase  being  most 
abundant,  but  some  microcline  can  be  distinguished  75 

6.  Red  shale   .  10 

7.  Thin-bedded  red  and  white  sandstone,  finer  grained 

than    the    higher    layers.     Under    the  microscope. 
•  (Plate  XVI,  B,  p.  72)  it  is  seen  that  less  than  half 

is  quartz.    The  orthoclase  feldspars  are  much  altered, 
but  some  plagicclase  was  seen.    There  is  consider- 


able mica.    The  cement  is  mainly  calcite       .       .  3 

8.  Main  Shale  Bed.    Red  shale  with  thin  partings  of 

hard  greenish  sandstone,  and  some  grit  towards  the 
base.    Thickness  not  accurately  known  on  account 

of  faulting  (see  Plate  XVII,  A,  p.  74)      .       .       .  45 

8Mi.  Red  and  green" shale  with  ripplemarks        .       .  4.5 

9.  Grit  and  shale  series.    Grit       .....  .5 

10.  Red   shale   3.0 

11.  White  grit   3.0 

12.  Red  shale  with  greenish  spots,  ripple  marks  and  rain 

prints    (Specimen   11316)   14.0 

13.  Grit,  mostly  light  colored    ......  .75 

14.  Red  shale   .     .       .  .25 

15.  Grit   2.0 

16.  Red  shale   .25 

17.  Grit   .35 

IS.  Red  shale   .35 

19.  Grit   1.0 


i  Below  this  the  numbering  of  the  beds  agrees  with  Winchell's  sec- 
tion. 


72 


RELATION  OF  SANDSTONES. 


20.  Red  shale,  mud  cracks       .       .        .       .       .       .  3.5 

21.  Grit,  white,  quite  calcareous  from  decomposition  of 

basic  feldspars         .       .       .       .       .       .       .  1.5 

22.  Red  shale  and  shaley  sandstone,  with  green  layers  and 

ripple  marks    .        .        .       .       .       .       .        .  14. 0 

23.  Light  red  sandstone    .        .       .        .               .        .  3.0 

24.  Red  grit,  some  white   4.5 

25.  Shaley  red  sandstone,  very  hard;  some  white    .        .  10.0 

26.  Red  grit     v\     .;     ;  .       .       .       .       .       v      .  3.5 

27.  Dark  red  shale  and  shaley  sandstone       .        .        .  9.0 

28.  Lighter  colored  sandstone  (white  and  red)        .        .  8.0 

29.  Green  shale,  ripple  marks    .        .        .        .        .        .  5.0 

30.  Red  shale  and  shaley  sandstone,  ripple  marks    .        .  9.0 

31.  Grit   with   shale   layers   4.0 

32.  Red  and  white  mottled  cross-bedded  sandstone    .        .  5.0 

33.  Grit  and  conglomerate,  coarsest  in  middle    .        .        .  7.0 

34.  Shaley  micaceous  sandstone;  pinches  out    .        .        .  .75 

35.  Grit   .85 

36.  Red  shale   .35 

37.  Grit    '   2.0 

38.  Red  shale    .        .        .        .        .       .        .       .        .  .2 

39.  Greenish  grit       .        .        .        .        .        .        .        .  .5 


40.  Red  and  white  sandstone,  pinches  out  into  conglom- 
erate. Under  microscope  (Specimen  11300)  shows 
that  over  three-quarters  of  the  rock  is  quartz.  Re- 
mainder includes  feldspars,  mainly  orthoclase,  al- 
though both  microcline  and  plagioclase  were  distin- 
guished, mica,  and  rarely  ferromagnesian  minerals. 
Average  size  of  the  grains  is  about  .25  mm.  but  there 


is  much  variation.    All  are  subangular    .        .        .  1.2 

41.  Red  grit  passing  below  into  coarse  light  colored  sand- 

stone; cross-bedded    .        .        .       .       .        .       .  3.5 

42.  Red  conglomerate,  coarser  below;  pebbles  up  to  two 

inches       .....       .    -  .       .       .  7.0 

43.  Red  shale  with  green  spots;  some  conglomerate       .  1.5 

44.  Firm  light-colored  conglomerate  with  enclosed  layers 

of   cross-bedded   sandstone      .        .        .        .        .  3.0 

45.  Green  and  red  shale,  micaceous  ■  .        .        .  .7 

46.  Sandy  shale  1.0 

47.  Fine  red  shale,  ripple  marks  15. 0 

48.  Quartz  Conglomerate.    Coarse  hard  pyritiferous  con- 

glomerate.   Color   usually   white   to   greenish.  In- 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.       Bulletin  No.  XXV,  Plate  XVI. 
Photomicrographs  in  Ordinary  Light,  Magnified  12  Diameters. 


A.  Vei-y  fine-grained  greenish  calcareous  shaley  sandstone  from  Middle  River, 
bed  1,  Amnicon  formation  (specimen  8611).  The  light-colored  grains  are  fine 
angular  quartzes,  averaging  .01  mm.  in  diameter.  An  occasional  feldspar  is 
seen,  and  mica  is  visible  in  the  hard  specimen.  The  matrix  of  the  rock  is 
crystalline  calcite,  which  in  one  place  forms  a  vein  in  which  its  characteristic 
cleavage  may  be  seen.  A  chemical  analysis  shows  CaO  10.7l9o,  MgO  0.12%, 
which  would  require  8.55%  CO,  making  a  total  of  about  19%  of  carbonate  (see 
p.  52). 


B.  Fine-grained  arkose  sandstone  from  Amnicon  formation,  bed  7.  St.  Louis 
River  (specimen  11.321).  Quartte  constitutes  a  little  less  than  half  of  the  rock. 
The  remainder  is  feldspar  (mainly  orthoclase.  but  some  more  basic  varieties), 
with  iron  oxide,  a  little  mica,  and  calcite  cement. 


RELATION  OF  SANDSTONES.  73 

eludes  layers  of  shaley  sandstone,  red  conglomerate 

and  red  or  green  shale       ......  50 

49.  Conglomerate,  somewhat  coarser  and  very  hard.  The 
pebbles  are  of  vein  quartz,  slate,  quartzite,  and  iron 
formation.  But  one  trap  pebble  was  found.  A  foot 
of  green  shale  is  found  in  places  next  to  the  under- 
lying slate         .        .        .....        .  100 


Total  thickness         ........  727 

Total  thickness  computed   from  dip   and   allowing  for 

faults  730 

Huronian 


50.  Thomson  slates.    Gray  slate  Unknown 

A  number  of  wells  in  Superior1  disclose  a  similar  succession. 
The  result  of  the  southeasterly  dip  of  the  sandstones  is  that 
while  in  East  Superior  solid  brownstone  is  found,  along'  the  St. 
Louis  River  to  the  west  there  is  only  discovered  red  sandy  shale, 
carrying"  a  little  salt  water.  The  deepest  well  of  which  the  record 
was  obtained,  is  Patterson's,  in  N.  E.  %  of  N.  E.  %  of  Sec.  24, 
T.  49,  R.  14  W.  (see  general  map).  This  penetrates  185  feet  of 
dry  drift,  below  which  was  found  over  700  feet  of  red  sandy 
shale,  undoubtedly  belonging  to  the  Amnicon  formation. 

Summary.  The  exposures  described  above  show  that  the 
stratigraphic  sequence  of  a  downward  gradation  through  pro- 
gressively more  and  more  arkose  sandstone  into  red  shales,  some- 
times interbedded  with  conglomerate  and  grit,  is  found  through- 
out the  district.  In  the  case  of  the  exposures  on  Middle  and 
St.  Louis  rivers  it  is  practically  certain  that  the  upper  beds 
belong  to  the  Bayfield  group.  On  the  other  hand,  in  the  case  of 
the  Fish  Creek  section,  farther  east,  the  lower  beds  plainly  be- 
long in  the  Oronto  group,  and  are  seen  to  grade  upward  into 
sandstones  which  are  correlated  with  the  Bayfield  group.  These 
facts  indicate  that  the  Bayfield  and  Oronto  groups  are  conform- 
able and  hence  should  both  be  placed  in  the  Upper  Keweenawan 
series. 


i  Records  furnished  by  J.  A.  Colwell,  a  well-driller,  1900,  and  Prof. 
J.  A.  Merrill,  1910. 


74 


RELATION  OF  SANDSTONES. 


The  only  alternative  is  to  suppose  that  the  Bayfield  group 
rests  unconformably  upon  the  Oronto  group,  somewhere  beneath 
the  drift-covered  interval  at  the  head  of  Chequamegon  Bay. 
While  this  cannot  be  disproved,  there  is  nevertheless  no  evidence 
of  any  kind  to  indicate  that  such  is  the  case  and  on  such  an  hy- 
pothesis must  rest  the  burden  of  proof. 

Categorically  the  evidence  may  be  stated  as  follows: — 

1.  The  same  conformable  downward  gradation  from  more 
quartzose  into  more  feldspathic  sandstone  and  red  shale  is  found 
at  several  widely  separated  localities  within  the  district. 

2.  At  most  of  these  localities  the  identification  of  the  upper 
beds  with  the  Bayfield  group  is  indisputable. 

3.  On  Fish  Creek  the  correlation  of  the  lower  beds  with  the 
Oronto  group  is  almost  equally  definite,  thus  indicating  that  the 
lower  beds  at  other  places  are  presumably  the  top  of  the  Oronto 
group. 

4.  No  debris  worn  from  the  rocks  of  the  Oronto  group  has 
been  found  in  rocks  of  the  Bayfield  group.  For  the  most  part 
the  younger  sandstones  are  made  up  of  grains  which  average 
somewhat  larger  in  size  than  those  of  the  Oronto  group,  thus 
showing  that  the  materials  of  the  Bayfield  group  must  in  any 
event  have  been  largely  derived  from  other  sources  than  those 
of  the  Oronto  group. 

5.  There  is  no  universal  structural  difference  between  the 
two  groups.  The  Bayfield  group  lies  in  the  center  of  the  Lake 
Superior  synclinorium  and  hence  is  usually  nearly  horizontal ; 
but  near  Superior,  all  along  the  great  fault  of  the  Douglas  trap 
range,  and  apparently  on  Fish  Creek,  it  was  involved  in  the 
extensive  folding  and  faulting  formerly  supposed  to  be  con- 
fined to  the  Oronto  group. 

6.  If  the  Bayfield  group  is  unconformable  upon  the  Or- 
onto group,  then  its  lowermost  exposed  m'ember  is  indistinguish- 
able on  lithologic  or  structural  grounds  from  the  recognized 
Oronto  group. 

There  is,  therefore,  no  reason  to  place  the  Bayfield  and  Oronto 
groups  in  different  periods,  and  the  evidence  at  hand  drives  us 
to  the  conclusion  that  the  Bayfield  group  is  a  part  of  the  Upper 
Keweenawan  series. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.       Bulletin  No.  XXV,  Plate  XVII. 


A.  North  bank  of  St.  Louis  River,  near  line  between  St.  Louis  and  Carlton 
counties,  Minnesota.  The  cliff  exposes  red  shale,  with  thin  greenish  sandstone 
partings.  This  is  a  part  of  the  Amnicon  formation.  A  normal  fault  of  at  least 
40  feet  displacement  passes  through  the  east  end  of  the  exposures  (see  p.  91). 


B.  West  bank  of  Middle  River,  Sec.  25,  T.  18,  R.  12  W.,  Douglas  County, 
showing  contact  between  the  Middle  Keweenawan  traps  at  left  of  ravine,  and 
overturued  beds  of  red  and  greenish  feldspathic  sandstoue  and  shale  of  the  Am- 
nicon formation  to  right  (see  fate  XIII,  p.  66). 


CONTACT  WITH  TRAPS. 


75 


CHAPTER  VI 


THE  CONTACT  OF  THE  BAYFIELD  GROUP 
WITH  THE  TRAPS 


General  Statement.  All  along  the  south  coast  of  the  west 
end  of  Lake  Superior  the  Bayfield  group  of  sandstones  comes 
into  contact  with  the  traps  of  Middle  Keweenawan  age,  with  dip 
to  the  southeast  at  angles  varying  from  10  to  70  degrees.  At 
the  head  of  the  lake,  on  St.  Louis  River,  near  the  western  border 
of  the  state,  the  conformable  downward  extension  of  this  group, 
the  Amnicon  formation,  appears  from  beneath  the  younger  sand- 
stones and  is  plainly  in  unconformable  contact  with  the  under- 
lying slates  of  Huronian  age. 

Douglas  Fault.  It  has  long  been  recognized  that  the  con- 
tact of  the  Bayfield  group  with  the  traps  of  the  Douglas  (or 
South)  Range  is  marked  by  a  fault.  "With  regard  to  the  age, 
extent,  and  significance  of  this  displacement  there  has  been  much 
diversity  of  opinion.  As  explained  in  Chapter  III,  Irving  was 
of  the  opinion  that  the  contact  was  an  unconformity  along  a 
fault  scarp  complicated  by  slight  recent  movement  on  the  same 
plane.  Since  that  time,  Grant  recognized  that  an  enormous 
displacement  has  taken  place  since  the  deposition  of  the  sand- 
stone, and  that  the  fault  is  of  the  thrust  type  (see  p.  89). 

LOCAL  DETAILS 

On  Iron  River,  near  the  eastern  boundary  of  Bayfield 
County,  is  the  most  easterly  known  exposure  of  the  traps  of  the 
South  or  Douglas  Range.  Several  miles  west  of  this  small  out- 
crop, the  crest  of  the  Douglas  trap  range  rises  above  the  plain 


76 


CONTACT  WITH  TRAPS. 


of  Pleistocene  deposits  (see  p.  7,  and  Plate  II,  p.  8).  Where 
Brule  River  crosses  through  a  deep  gap  in  this  ridge,  the  contact 
of  the  sandstone  and  trap  is  not  exposed ;  it  occurs  beneath  a  cov- 
ered space  of  about  a  fourth  of  a  mile.  No  distinct  ev1  lence  of 
faulting  or  other  disturbance  appears  at  this  point  in  either  for- 
mation. A  contact  showing  fine  conglomerate  was  reported  by 
Sweet1  (see  p.  44),  in  Sec.  30,  T.  48,  R,  10  W.  This  locality 
was  visited  by  Grant's  party,  but  the  exposure  was  not  found. 

Middle  River  Contact.  Ten  miles  west  of  the  Brule,  Mid- 
dle River  exposes  the  contact  of  the  traps  and  the  Amnicon 
formation,  which  conformably  underlies  the  Bayfield  group 
(see  p.  66).  Berkey,  Van  Hise,  and  Grant  visited  this  locality 
in  1899  and  made  the  map  which  is  the  basis  of  Plate  XIII. 
They  recognized  the  true  bedding  of  the  sandstone,  which  Sweet 
had  not,2  and  assumed  that  the  structure  was  anticlinal.  (See 
also  Plate  XVII,  B,  p.  74,  and  Plate  XXI,  p.  90). 

The  writer  decided  that  this  interpretation  must  be  an  error, 
since  the  strati  graphic  sequence  observed  in  other  localities  is 
exactly  opposite  to  that  required  by  such  an  hypothesis  (see  sec- 
tion on  p.  67).  No  evidence  could  be  detected  of  a  small  syn- 
cline  next  to  the  fault  at  the  eastern  exposure,3  such  as  would  be 
expected  below  a  thrust  fault.  The  fault  cuts  the  E-W  strike' 
of  the  fold,  the  layers  in  which  are  somewhat  broken  near  the 
contact.  Furthermore,  as  explained  on  p.  68,  ripple  marks  are 
found,  which  clearly  demonstrate  that  the  southward-dipping 
beds  have  been  overturned.  The  structure  deduced  from  these 
facts  is  that  of  an  overturned  and  broken  anticline,  a  normal 
structure  in  connection  with  a  thrust  fault  ;  while  that  described 
by  Grant  would  be  unusual. 

1  Sweet,  E.  T.,  Geol.  of  Wis.,  1873-9,  vol.  ill,  p.  348. 

Irving,  R.  D.,  Copper-Bearing  Rocks,  Mon.  U.  S.  G.  S.,  vol.  V,  1883, 
p.  257. 

2  Sweet,  E.  T.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  347. 

3  Grant,  U.  S.,  Copper-Bearing  Rocks  of  Douglas  Co.,  Wis.  Geol.  & 
Nat.,  Hist.  Survey,  Bull.  VI,  1801,  structure  section  C-D  on  Plate  IX, 
p.  31. 

  Junction  of  Lake  Superior  Sandstone  and  Keweenawan  Traps 

in  Wis.,  Bull.  Geol.  Soc.  of  America,  vol.  13,  1906,  p.  8. 
Personal  communications. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey. 


Bulletin  No.  XXV,  Plate  XVIII. 


A.  East  bank  of  Amnicon  River,  Sec.  29,  T.  48,  R.  12  W.,  Douglas  County, 
showing  thrust  fault,  which  brings  the  traps  into  contact  with  the  Orienta  sand- 
stone. 


B.  Key  to  the  foregoing  photograph. 


COy TACT  WITH  TRAPS. 


77 


Amnicon  River  Contact.  Where  Amnicon  River  crosses  the 
fault,  occur  good  exposures  which  bring  to  light  the  actual  plane 
of  contact.1  Changes  in  the  course  of  the  stream  have  resulted  in 
uncovering  the  formations  for  a  considerable  distance,  as  shown 
in  Fig.  10.  These  exposures  are  particularly  interesting,  in 
that  they  show  the  direction  of  the  fault  to  change  abruptly 
from  nearly  E.  and  W.  to  N.  70°  E. 

The  eastern  exposure,  which  doubtless  was  at  one  time  a  chan- 
nel of  the  river,  is  in  a  deep  and  narrow  ravine  following  the 


j      Orient  a  Jan  ch  tone             ^  y 

Q  5  L 

ZQ 

FAULT 

Fig.   10.    Sketch  map   showing  contact   of   trap   and   sandstone   on  Amnicon 
River,  Douglas  County. 

contact  for  some  distance.  The  actual  junction  is  covered  with 
but  a  few  inches  of  soil.  The  south  side  of  the  ravine  is  an 
overhanging  wall  of  brecciated  trap.  In  the  bottom,  occasionally 
rising  into  ridges,  and  on  the  north  wall,  occur  exposures  of 
conglomerate  with  interbedded  layers  of  sandstone.  The  dip  of 
the  beds  varies  from  vertical  to  about  45°  N. ;  but  the  exact  rela- 
tion of  the  horizontal  sandstone  farther  to  the  north  could  not 
be  determined  because  of  fallen  debris  and  the  irregular  shear- 
ing that  conceals  the  true  bedding.  It  is  probably  marked  by- 
faulting,  as  will  presently  be  explained.  The  conglomerate  is 
composed  of  trap  pebbles,  usually  much  weathered,  averaging 
an  inch  or  twTo  in  diameter,  but  with  occasional  specimens  a  foot, 
in  diameter.  All  are  well  rounded,  and,  so  far  as  was  ascer- 
tained, composed  mainly  of  porphyry  and  amygdaloids.  The 


i  Sweet,  E.  T.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  346. 
Grant,  U.  S„  Copper-Bearing  Rocks,  p.  ]9. 


78 


COy TACT  WITH  TRAPS. 


sandstone  matrix  and  interbedded  layers  do  not  differ,  except  in 
coarseness  of  grain,  from  the  rock  exposed  to  the  north  (p.  43)  ; 
some,  however,  appear  to  contain  more  small  fragments  of  trap. 
At  the  west  end  of  the  ravine  is  exposed  a  thin  la}Ter  of  hard 
ferruginous  sandstone.  It  forms  the  face  of  the  north  wall, 
dipping  south  at  approximately  the  same  angle  as  the  fault 
(about  45°),  thus  cutting  across  the  vertical  layers  of  conglo- 
merate and  sandstone  beneath.  On  the  upper  surface  of  this 
layer  are  two  sets  of  grooves;  one  is  parallel  to  the  dip,  the 
other  is  inclined  at  an  angle  of  about  30°  in  a  NE-SW  direction. 

The  exposures  are  naturally  much  better  on  the  present  banks 
of  the  stream  to  the  west  (Plate  XXII,  B,  p.  92).  That  this 
present  course  has  not  been  occupied  by  the  river  for  a  great 
length  of  time,  is  shown  by  the  fact  that  the  fall  of  about  15 
feet,  just  at  the  fault  line,  has  receded  but  slightly  into  the 
traps.  Plate  XVIII  shows  the  eastern  wall  of  the  gorge.  Two 
faults  are  seen,  of  which  the  upper  or  southern  one  dips  38°  S. 
with  an  E-W  strike;  the  lower  46°  S,  strikes  N.  72°  E.  They 
are  separated  by  a  zone  of  trap  breccia,  such  as  also  occurs  be- 
neath much  of  the  bottom  of  the  ravine  to  the  east,  as  above 
described.  It  consists  of  angular  and  subangular  fragments  of 
weathered  trap,  some  of  them  several  feet  across.  North  of  the 
lower  fault  occurs  a  wedge  of  conglomerate,  bounded  on  the 
north  by  an  approximately  vertical  plane.  In  this  conglomerate 
are  two  thin  sandstone  layers  striking  parallel  to  this  fault,  and 
dipping  south  at  a  somewhat  steeper  angle  than  the  fault.  The 
southern  one  is  almost  quartzite,  and  the  other  carries  scratches 
like  those  noted  to  the  east.  The  bedding  of  the  conglomerate  is 
otherwise  indistinguishable.  In  places  to  the  north  it  appears  to 
be  vertical,  as  shown  by  an  interbedded  sandstone  layer;  but 
there,  with  no  appearance  of  fracture,  the  conglomerate  gives 
-way  above  to  horizontal  thin-bedded  quartz  sandstone,  and  below 
-.to  eross-bedded  pebbly  white  sandstone,  among  the  pebbles  of 
which  are  some  of  quartz  and  quartzite.  There  an  appearance 
of  gradation  is  presented,  but  above  the  contact  is  sharp.  Shear- 
in^makes  the  relations  difficult  to  determine.  Above  the  top  of 
the  conglomerate  the  foot  wall  of  the  fault  is  composed  of  much 
fractured  sandstone.  About  100  feet  to  the  north  a  small  thrust 
fault  of  undetermined  throw  is  seen  in  the  sandstone,  as  shown 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.     Bulletin  No.  XXV,  Plate  XVIIIa. 


A.  Lower  Falls,  Amnicon  River,  Douglas  County  (see  Fig.  10,  for  location). 
Looking  north,  showing  Copper  Creek  beds  of  Orienta  sandstone. 


B.  Diagram  (drawn  from  a  photograph)  of  part  of  west  bank  of  Amnicon 
River,  Douglas  County,  just  north  of  contact  of  trap  and  sandstone  (south  of 
the  falls  shown  in  A) — for  location,  see  Fig.  10.  This  exposure  shows  the  dying 
out  of  the  middle  fault  into  a  confused  zone  of  fractures  which  separates  the 
vertical  conglomerate  layers  from  the  horizontal  sandstone  to  the  north — shown 
at  the  right.  The  shearing  planes  in  the  vertical  layers  are  very  complex,  and 
are  but  partly  represented. 


CONTACT  WITH  TRAPS. 


79 


in  Plate  XXII,  A,  p.  92;  the  dip  is  38°  S.,  the  strike  about  N. 
55°  E. 

The  west  bank  is  not  so  well  exposed,  owing  to  a  recent 
fall  of  the  overhanging;  wall  of  trap,  thus  concealing  the 
main  fault.  Two  other  zones  of  displacement  may  be  seen  to 
the  north.  The  southernmost  of  these  is  important  since  it  shows 
the  relation  of  the  vertical  sandstone  and  conglomerate  to  the 
horizontal  sandstone  beds. 

It  is  not  clear  just  how  the  middle  fault  is  related  to  that 
described  on  the  other  side  of  the  river.  The  two  there  seen, 
appear  to  join  beneath  the  water,  so  that  no  well-defined  breccia 
is  seen  on  the  west  bank,  the  actual  contact  being  marked  only 
by  an  inch  or  so  of  red  shale.  The  middle  fault  of  the  west  bank 
branches  out  from  the  others  beneath  the  river.  It  is  composed 
of  several  irregular  planes  of  fracture,  as  is  shown  in  the  plate 
Between  the  two  faults  is  found  conglomerate  with  irregular 
interbedded  sandstone  layers,  all  much  sheared,  as  is  imperfectly 
shown  in  Plate  XVIII  a,  B,  p.  78.  A  remarkable  feature  is  the 
sudden  ending  of  one  of  the  conglomerate  layers  against  sand- 
stone below,  with  no  appearance  of  fracture.  Whether  or  not  the 
alternation  of  conglomerate  and  sandstone  represents  bedding,  is 
not  known ;  but  it  is  worthy  of  note  that  no  conglomerate  is  found 
in  undisturbed  sandstone  beds,  while  most  of  the  layers  occupy  a 
vertical  or  highly  tilted  attitude  and  are  much  sheared.  This  in- 
tense shearing  is  quite  irregular ;  no  permanent  system  could  be 
discovered,  although  many  of  the  planes  of  fracture  dip  toward 
the  fault  at  a  low  angle.  In  the  western  bank  the  northernmost 
fault  is  again  seen,  dipping  to  the  south  at  an  angle  of  28°. 

There  are  but  poor  exposures  in  the  wide  valley  that  crosses 
the  fault  to  the  west  of  the  river.  The  inclined  conglomerate 
beds  reappear,  but  their  relation  to  the  horizontal  beds  to  the 
north  is  not  clear  on  account  of  the  intense  shearing ;  no  pebbles 
extend  beyond  their  limits.  Fractures  approximately  parallel  to 
the  fault  are  most  abundant,  apparently  representing  the  dying 
out  of  the  middle  fault.  The  strike  of  the  contact  is  here  N.  70° 
E.  while  that  of  the  conglomerate  is  N.  50°  E.1 


i  About  a  quarter  of  a  mile  to  the  west  is  a  valley  which  crosses  the 
contact  and  is  believed  to  show  exposures;  the  writer  was,  however, 
unable  to  visit  it. 


.80 


CONTACT  WITH  TRAPS. 


Copper  Creek.  In  sec  15,  T.  47,  R.  14  W.,  Copper  Creek 
crosses  the  contact  of  the  sandstones  with  the  traps.  The  actual 
junction  is  covered  by  a  few  feet  of  debris,  so  that  the  attitude 
of  the  fault  plane  is  difficult  to  determine.1  Sweet's  section 
shows  it  dipping  to  the  north,  but  the  writer  was  inclined  to 
believe  that  the  dip  is  about  60°  to  the  south.  The  sandstone  is 
sheared  and  sharply  flexed  for  a  distance  of  less  than  a  hundred 
feet  from  the  contact,  thus  indicating  an  upward  movement  of 
the  igneous  rocks.  No  conglomerates  or  other  unusual  features 
are  found  in  the  sandstone. 

Palls  of  Black  River.  What  is  probably  the  best  known 
exposure  of  the  sandstone-trap  contact  is  that  in  the  S.  E.  y± 
sec  21,  T.  47,  R.  14  W.,  at  the  picturesque  falls  of  Black  River. 
The  locality  is,  however,  more  attractive  for  its  scenery  than  for 
its  rocks,  for  the  latter  are  not  everywhere  well  exposed.2  Plate 
XIX  is  a  map  of  this  locality  made  by  Grant  in  1899,  and  shows 
the  complex  relations  of  the  formations  more  clearly  than  could 
any  description. 

Conglomerate  is  found  in  but  two  places.  The  pebbles  are 
decayed  acid  lavas,  vein  quartz,  and  red  quartzite,  preserving 
about  the  same  proportions  as  the  pebbles  in  the  main  body  of 
the  sandstone.  The  sizes,  however,  average  somewThat  larger, 
pebbles  six  inches  in  diameter  being  found. 

On  the  east  bank,  not  far  above  the  stream  and  beneath 
trap  layers  higher  up  the  bank,  is  a  ledge  of  conglomerate  with 
two  interbedded  sandstone  layers  which  dip  30-40°  N.  This  is 
quite  close  to  the  main  fault  (which  here  dips  some  50°  S.)  and 
to  the  supposed  cross  fault.  Above  the  conglomerate,  sandstone, 
bearing  but  occasional  pebbles,  approaches  close  to  the  fault. 

On  the  west  bank  of  the  stream  is  a  larger  ledge  of  conglomer- 
ate and  sandstone.  The  clip  here  is  reversed,  being  about  10  to 
20  degrees  to  the  southeast.  This  feature  is  shared,  as  may  be 
seen  in  the  diagram,  by  a  number  of  sandstone  exposures  to  the 

1  Sweet,  E.  T.,  Geol.  of  Wis.,  vol.  Ill,  1873-9,  p.  344. 
Grant,  U.  S.,  Copper  Bearing  Rocks,  p.  19. 

2  Sweet,  E.  T.,  Geol.  of  Wis.,  vol.  Ill,  1873-9,  p.  340. 
Grant,  U.  S.,  Copper  Bearing  Rocks,  p.  19. 


Wisconsin  Geol.  and  Nat.  Hist.  Survey. 


Bulletin  No.  XXV,  Plate  XIX. 


Man.,  of  vicinity  of  Lower  Falls  of  Black  River,  Douglas  County,  showing  contact  of  Middle  Ke- 
wee^  Wan  traps  and  Drienta  sandstone.  Map  by  U.  S.  Grant,  1899 ;  sections  by  F.  T.  Thwaites, 
1910.    Contour  interval,  20  feet ;  elevations,  11  feet  too  high. 


CONTACT  WITH  TRAPS. 


81 


west.  All  of  these  rocks  are  quartzose,  like  those  to  the  north, 
the  only  difference  being  that  they  are  considerably  harder. 

Above  these  exposures  rises  a  cliff  of  trap  breccia,  in  which 
are  included  several  large  pieces  of  red  quartzite.  The  extent 
of  the  brecciation  is  much  greater  than  noted  elsewhere,  extend- 
ing several  hundred  feet  from  the  contact.  The  dip  of  the 
fault  here  cannot  be  measured,  but  appears  to  be  not  very  steep. 

The  sandstone  north  of  a  line  bounding  these  south-dipping 
exposures,  as  usual  dips  to  the  north.  These  beds  are  described 
on  p.  44. 

A  study  of  the  detailed  map  shows  that  the  reentrant  in  the 
fault  line  must  be  the  cause  of  the  abnormal  features  here  noted, 
just  as  the  bend  in  the  reverse  directiuri  at  the  Amnicon  River  is 
accompanied  by  peculiar  phenomena.  There  must  be  a  cross 
fault  to  account  for  this  reentrant  angle  in  the  border  of  the 
trap ;  the  excessive  brecciation  is  doubtless  due  to  its  presence.  It 
is  most  probable  that  the  south-dipping  layers  of  sandstone  are 
separated  from  the  north-dipping  by  a  continuation  of  the  fault 
to  the  east  of  this  break.  This  fault  probably  passes  through 
the  poor  exposures  on  the  west  side  of  the  valley,  although  they 
are  so  obscure  that  nothing  can  be  stated  positively;  it  may, 
however,  join  the  main  or  southern  fault  beneath  a  covered  space 
farther  to  the  east.  The  writer  could  distinguish  no  definite 
evidence  of  unconformity,  or  of  this  reentrant  being  a  sinuosity 
of  an  ancient  shore  line,  as  supposed  by  Irving.1 

In  the  S.  E.  *4  of  the  N.  W.  %  of  sec.  29  of  the  same  town- 
ship occurs  a  small  exposure  of  the  contact.  Irregularly-sheared 
sandstone  occurs  within  two  feet  of  trap  breccia  and  dips  about 
40°  N.  for  a  short  distance  from  the  contact. 

Interpretation  of  Exposures.  Irving  believed  that  the  phe- 
nomena above  described  represented  an  unconformity  along  a 
fault  scarp,  complicated  by  a  slight  amount  of  recent  faulting 
on  the  same  plane.  Grant  discovered  the  great  amount  of  throw 
(at  least  3,000  feet;  see  p.  66)  which  the  fault  possesses,  and 
declared  the  evidence  to  be  not  conclusive  in  favor  of  uncon- 


i  irving,  R.  D.,  Copper-Bearing  Rocks,  Mon.  U.  S.  G.  S.,  vol.  V,  1883, 
p.  441. 


6 


82 


CGXTACT  WITH  TRAPS. 


formity.  All  former  investigators  have  assumed  that  the  sand- 
stone was  a  marine  deposit,  a  fact  now  regarded  as  decidedly 
doubtful. 

The  following  evidences  favor  the  older  view : 

1.  The  presence  of  conglomerates,  often  of  large  pebbles  main- 
ly, if  not  sometimes  wholly,  derived  from  the  rocks  of  the  adja- 
cent trap  series. 

2.  The  striking  difference  in  the  amount  of  folding  and  met- 
amorphism  of  the  two  groups  of  rocks,  which  implies  that  most 
of  the  deformation  of  the  traps  must  have  taken  place  before 
the  deposition  of  the  younger  sandstones. 

3.  The  enormous  throw  and  subsequent  erosion  required  by 
the  fault  hypothesis. 

4.  No  strata  are  known  from  which  the  conglomerates  might 
have  been  faulted  up ;  these  is  little  to  show  definitely  that  they 
have  been  faulted  up  more  than  a  few  feet. 

5.  The  dip  of  the  fault  plane  to  the  south,  giving  it  a  large 
horizontal  component  of  motion,  would  have  cut  away  a  large 
part  of  the  coarse  deposits  adjacent  to  the  fault  scarp,  thus  ex- 
plaining the  absence  of  conglomerate  at  some  points. 

6.  As  the  fault  is  part  of  the  Keweenawan  deformation,  rep- 
resenting a  broken  fold,  it  is  quite  probable  that  faulting  began 
before  the  time  of  deposition  of  the  adjacent  sandstone,  and  per- 
haps continued  through  the  time  of  its  formation. 

7.  The  Bayfield  sandstones  may  be  areally  continuous  with  the 
horizontal  light-colored  sandstones  of  the  Mississippi  valley  (cf. 
p.  58),  which  are  separated  from  the  tilted  Middle  Keweenawan 
by  a  considerable  unconformity. 

The  following  facts  support  the  Idea  that  the  faulting  is  in 
large  part,  if  not  wholly,  later  than  the  deposition  of  the  sand- 
stone : 

1.  Well  defined  conglomerates  occur  at  but  two  localities  out 
of  the  eight  known  exposures  (less  definite  ones  occur  at  two 
others) . 

2.  They  are  never  found  over  a  few  rods  from  the  contact. 

3.  They  do  not  clearly  grade  into  the  adjacent  sandstone. 

4.  They  occur  only  at  points  of  unusual  minor  faulting  in  the 
sandstone. 


CONTACT  WITH  TRAPS. 


83 


5.  No  patches  of  sandstone  are  found  resting  uncomformably 
upon  the  trap. 

6.  The  amount  of  conglomerate  is  not  sufficient,  nor  are  the 
pebbles  large  or  angular  enough,  to  be  regarded  as  either  a 
subaerial  or  marine  deposit  along  a  fault  scarp. 

7.  In  many  cases  the  pebbles  are  one-third  vein  quartz  and 
quartzite ;  these  could  only  have  been  supplied  from  a  distant 
source,  and  would  not  be  likely  to  occur  along  a  fault-scarp.  The 
trap  pebbles  were  not  usually  derived  from  the  immediately  ad- 
jacent rocks. 

8.  The  inclination  of  the  fault  plane  involves  a  large  horizon- 
tal component,  approximately  equal  to  the  vertical  one.  If 
faulting  took  place  during  or  just  prior  to  the  deposition  of  the 
sandstone,  this  would  involve  a  shifting  northward  of  the  scarp 
line,  thus  supplying  a  large  amount  of  fresh  unweathered  sed- 
iment. No  such  amount  of  sediment  of  that  character  is  found 
in  the  upper  beds  of  the  sandstone. 

9.  The  throw  of  the  fault  since  the  deposition  of  the  sand- 
stone is  certainly  great ;  it  must  be  at  least  3,000  feet,  since  that 
thickness  of  strata  is  involved  on  Middle  River. 

10.  The  total  displacement  involved,  even  if  the  traps  are  as 
thick  as  was  formerly  supposed  (see  p.  89),  is  not  greater  than 
that  of  many  well-known  thrust  faults.  The  uplifted  rock  may 
readily  have  been  eroded  during  the  long  time  that  has  since 
elapsed. 

11.  The  conglomerates  that  occur  are  so  intensely  sheared 
that  they  may  represent  material  from  lower  conglomerates 
which  has  been  dragged  up  along  the  fault  and  worked  into  the 
sandstone,  like  the  layers  of  sandstone  that  have  been  found  in- 
cluded in  the  trap  breccia  (see  p.  81).  This  hypothesis  would 
explain  some  of  the  peculiar  features  of  the  conglomerates,  found 
only  at  points  of  intense  faulting.  We  have  no  knowledge 
of  the  stratigraphy  of  the  lower  beds  of  the  sandstone  in  this 
part  of  the  area,  but  conglomerates  almost  undoubtedly  occur 
at  lower  horizons. 

12.  At  several  points,  cross-bedded  layers  in  the  sandstone 
dip  toward  the  fault.  This  would  be  an  unusual  occurrence 
if  the  rocks  occupied  the  same  relative  positions  at  the  time  of 
the  deposition  of  the  sandstone,  as  they  do  today. 


84 


CONTACT  WITH  TRAPS. 


13.  The  areal  connection  of  the  Bayfield  group  with  the  Cam- 
brian sandstones  of  Minnesota  is  not  proved ;  the  age  and  struc- 
tural relations  of  the  red  sandstones  beneath  the  light-colored 
Potsdam  of  Minnesota  are  unknown  (cf.  p.  58). 

14.  If  the  supposed  fault  scarp  was  being  eroded  during  the 
deposition  of  the  sandstones,  then  the  sandstones  must  have 
been  formed  very  soon  after,  if  not  during  a  period  of  regional 
deformation.  This  contrasts  them  sharply  with  those  of  the 
recognized  Cambrian  of  southern  "Wisconsin,  which  were  evi- 
dently formed  under  quiescent  conditions  (cf.  p.  101). 

15.  The  sandstones  adjacent  to  the  fault  (Bayfield  group) 
are  apparently  conformable  upon  those  which  overlie  the  traps 
(Oronto  group)  and  elsewhere  are  folded  with  them.  They  all 
belong  to  the  same  period  of  deposition.  Therefore  it  is  very 
improbable  that  'the  exposures  described  above  represent  an  un- 
conformity involving  any  great  lapse  of  time.  If  there  is  any 
unconformity,  it  is  rather  a  local  matter  formed  by  slight  move- 
ments of  the  fault  during  the  deposition  of  the  sandstones. 

The  writer  concludes  that  inasmuch  as  deformation  appears 
to  have  been  more  or  less  continuous  throughout  Keweenawan 
time,  the  probabilities  are,  that  while  most  of  the  movement  on 
the  fault  may  have  been  accomplished  before  the  deposition  of 
the  sandstones  now  exposed,  that  slight  movements  may  have 
occurred  during  their  deposition,  while  a  considerable  amount 
has  demonstrably  occurred  since.  This  hypothesis  agrees  best 
with  all  that  is  known  of  the  phenomena  (cf.  p.  108). 

North  Coast  Contact.  Near  Duluth,  several  supposed  con- 
tacts of  the  sandstone  with  the  trap  came  to  the  notice  of  the 
writer.  Upon  investigation  they  proved  to  be  either  red  syenite, 
cemented  drift,  or  interbedded  Middle  Keweenawan  sediments. 
But  as  explained  on  p.  107,  it  is  entirely  possible  that  an  uncon- 
formable contact  may  yet  be  found. 

St.  Louis  River  Contact.  Although  on  St.  Louis  "River  the 
■Amnicon  formation  of  the  underlying  Oronto  group  is  seen  in 
contact  only  with  the  Huronian  slates,  the  presence  of  basic 
trap  pebbles  in  such  abundance  implies  a  nearby  exposure  of 
Keweenawan  igneous  rocks  during  deposition,  and  hence  a  pos- 
sible unconformity.  Less  than  a  mile  from  the  exposures  on 
Mission  Creek,  near  Fond  du  Lac,  hills  of  intrusive  gabbro  rise 


CONTACT  WITH  TRAPS. 


85 


to  a  level  some  500  feet  above  the  exposures.  About  the  middle 
of  the  interval  between  these  exposures,  some  real  estate  specu- 
lators at  one  time  drilled  a  deep  hole  in  search  of  natural  gas, 
the  log  of  which  is  here  given : 

LOG  OF  CHURN  DRILL  HOLE  NEAR  SHORT  LINE  PARK,  MINN. 

Situated  on  S.  line  Sec.  32,  T.  49,  R.  15  W.,  in  a  ravine  at  elevation 
900  feet  A.  T.  (After  N.  H.  Winchell,  Natural  Gas  in  Minnesota,  Minn. 
Geoi.  and  Nat.  Hist.  Survey,  Bull.  V,  1889,  p.  31;  Geology  of  Minnesota, 
Vol.  IV,  1899,  p.  567.) 

Pleistocene.  Thickness,  feet 

Drift    (clay?)    no  samples  100 

Ketveenawan 


2. 

Rock,  said  to  be  soft,  no  samples  .... 

131 

3. 

Brownish  red  shale  (called  tuff  by  Winchell) 

12 

4. 

"Decayed  trap",  perhaps  conglomerate 

33 

5. 

No  samples,  presumably  same  as  above 

104 

6. 

"Surface  eruptives",  perhaps  conglomerate  . 

37 

7. 

The  same,  samples  appeared  to  be  in  part  fragmental, 

hence  is  probably  a  conglomerate  .... 

31 

8. 

Gray  slate  or  shale,  said  to  be  misplaced  in  record,  but 
is  possibly  one  of  the  greenish  siliceous  shales  of  the 

Amnicon  formation     .        .  . 

15 

9. 

Pink  to  purple  quartz  sand  with  some  trap  fragments 

5 

10.  The  same  but  coarser  and  pyritiferous  with  pebbles  of 

trap    ..........  5 

11.  "Gray  slate",  probably  shale  rather  than  slate  misplaced 

in  the  record       ........  17 

12.  "Gabbro"   .  .16 

13.  Conglomerate  of  soft  trap  pebbles       ....  2 

14.  Pink  and  gray  quartzose,  pyritiferous  conglomerate  and 

quartzite  containing  pebbles  of  slate,  and  probably 
layers  of  shale    ........  20 

15.  "Surface  lavas  like  those  at  Duluth."    These  rocks  are 

clearly   igneous  .......  91 

Huronian-Thomson  Slate 

16.  Gray  and  black  quartzose  slate   930% 


Depth  of  hole  1,517% 

A  little  salt  water  was  found,  but  no  gas. 


86 


CONTACT  WITH  TRAPS. 


The  interpretation  of  the  foregoing  record  is  difficult.  Win- 
chell1  correlated  No.  14  with  the  similar  white  quartzose,  pyritif- 
erous  conglomerate  which  is  exposed  on  the  banks  of  St.  Louis 
River,  to  the  west.  He  believed  that  the  conglomerate  seen  in 
the  river  valley  was  older  than  the  Keweenawan  lava  flows,  since 
it  contains  no  trap  pebbles.  (One  large  one  was  found  by  the 
writer,  see  p.  70).  The  red  conglomerates  and  shales  of  the  St. 
Louis  River  section,  which  at  that  point  immediately  overlie 
the  pyritiferous  conglomerate,  he  held  to  be  either  separated  by 
an  unconformity  from  the  pyritiferous  conglomerate  or  to  have 
been  deposited  contemporaneously  with  the  traps.  The  inter- 
bedding  of  traps  and  conglomerates,  which  he  believed  was  shown 
in  the  above  drill  record,  fits  with  either  hypothesis.2  A  single 
pebble  of  pyritiferous  conglomerate  found  by  him  in  the  red 
trap  conglomerate,  was  believed  to  come  from  the  underlying 
conglomerate  and  therefore  to  indicate  an  hiatus  between  the 
deposition  of  the  two  conglomerates,  the  upper  one  of  which 
he  believed  to  be  of  pyroclastic  origin.  This  view  is  illustrated 
in  Plate  XX,  A. 

WincheH's  views  were  not  borne  out  by  the  writer's  investi- 
gations. It  seems  clear  that  there  is  no  unconformity  between 
the  two  types  of  conglomerate  on  St.  Louis  River.  The  pebble 
of  pyritiferous  conglomerate  found  in  the  upper  conglomerate, 
may  well  have  been  derived  from  some  other  similar  formation. 
Furthermore,  no  evidence  of  contemporaneous  volcanic  erup- 
tions was  discovered  in  the  Amnicon  beds  of  St.  Louis  River 
and  Mission  Creek.  These  sediments  do  not  differ  essentially 
in  character  from  the  other  parts  of  the  Oronto  group.  It  would 
therefore  appear  probable  that  the  pyritiferous  conglomerate 
found  in  the  drill  hole  is  not  the  same  as  that  on  the  river, 
but  is  a  part  of  the  Middle  Keweenawan  trap  series  with  which 
it  is  interbedded.  The  scarcity  of  coarse  trap  debris,  especially 
of  the  gabbro,  in  the  conglomerates  of  St.  Louis  River,  suggests 
that  faulting  since  the  formation  of  the  sediments  has  brought 
the  traps  into  their  present  position,  so  that  they  rise  500  feet 
or  more  above  the  river  level. 


1  Winchell,  N.  H„  Geol.  of  Minn.,  vol.  IV,  1899.  p.  15. 

2  Hall,  C.  W.,  Keweenawan  Area  of  E.  Minn.,  Bull.  Geol.  Soc.  of 
America,*  vol.  12,  1901,  p.  342. 


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CONTACT  WITH  TRAPS. 


87 


Still  another  explanation  of  the  pmbiguous  record  of  the 
Short  Line  Park  drill  hole  is,  that  all  the  strata  above  No.  15 
are  sediments,  the  drillings  from  coarse  conglomerates  having 
been  mistaken  for  traps  by  Winchell.  The  large  amount  of 
fragmental  material  noted  in  his  descriptions  of  the  drillings, 
supports  this  view.  Moreover,  a  resident  of  the  vicinity  who 
watched  the  drilling  informed  the  writer  that  a  daily  progress 
of  10  to  12  feet,  presumably  in  a  single  shift,  was  maintained 
with  the  use  of  1,500-pound  tools.  Such  a  rate  would  favor  the 
view  that  little  or  no  solid  trap  was  penetrated.  If  this  view 
(see  Plate  XX,  B)  is  correct,  there  may  not  be  any  fault  be- 
tween the  drill  hole  and  the  gabbro  bluffs,  the  conglomerates 
having  been  deposited  at  the  base  of  the  trap  hills.  The  scar- 
city of  gabbro  pebbles  in  the  drill  hole,  however,  strongly  in- 
dicates that  a  fault  occurs  between  the  drill  hole  and  the  bluff. 
Such  an  hypothesis  best  explains  the  present  relation  of  the 
gabbro  in  the  bluffs  to  the  north,  and  the  sediments  found  in  the 
drilling. 

Contact  with  the  Slates.  The  contact  of  the  Amnicon 'form- 
ation with  the  Thomson  slate,  on  St.  Louis  River,  demonstrates 
a  progressive  overlap.  As  shown  in  section  A-B,  on  the  gen- 
eral map,  the  traps  must  thin  out  and  be  overlapped  in  the  space 
between  the  Douglas  Range  and  this  point.  The  same  phenome- 
non must  also  occur  in  the  short  distance  between  Mission  Creek 
and  the  Short  Line  Park  bluffs  (see  p.  84). 

As  noted  in  the  last  chapter  (p.  72  ,  we  find  between  the  trap 
conglomerates  on  St.  Louis  River  and  the  underlying  slate  a 
pyritiferous  quartz  and  slate  pebble  conglomerate,  which  is 
clearly  part  of  the  Amnicon  formation.  The  surface  of  the  slate 
is  rough,  several  small  knobs  showing  through  the  conglomerate 
(see  Plate  XV,  p.  70). 


1 


88 


STRUCTURE. 


CHAPTER  VII 


THE  STRUCTURE  OF  THE  WISCONSIN 
COAST  OF  LAKE  SUPERIOR 


General  Statement.  The  basin  of  Lake  Superior  is  a  broad 
and  flat  synclinorium.  Toward  the  west  end  of  the  lake,  this 
structural  trough  turns  inland  up  Chequamegon  Bay,  and  thence 
crosses  Wisconsin  in  a  great  curve  to  the  St.  Croix  valley1  and 
into  Minnesota  (see  p.  60).  The  southward-dipping  Douglas  or 
South  Trap  range  divides  it  from  the  far  western  end  of  the 
lake,  which  is  bounded  on  the  north  by  the  south-dipping  traps 
of  the  Minnesota  or  North  range. 

The  Bayfield  and  Oronto  sandstone  groups  occupy  the  narrow 
•strip  between  the  north  escarpment  of  the  faulted  Douglas 
Range  and  the  lake,  lapping  across  the  course  of  the  traps  in  the 
promontory  of  the  Bayfield  Peninsula  and  the  Apostle  Islands, 
and  extending  into  the  basin  of  the  main  syncline  to  the  east. 
On  the  south  shore  the  sandstones  have  a  low  southeasterly  dip, 
a  continuation  of  the  inclination  of  the  traps  of  the  north  coast, 
passing  to  the  southeast  into  a  series  of  broad  open  folds  which 
occupy  the  bottom  of  the  synclinorium.  The  major  structural 
features  of  the  region  are  the  Douglas  Fault,  the  North  Coast 


i  Irving,  R.  D.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  1. 

  Copper-Bearing  Rooks.  U.  S.  G.  S.  Mon.  V,  p.  410,  with  struc- 
ture map  and  natural  scale  sections. 

Hall,  C.  W.,  Keweenawan  Area  of  E.  Minn.,  Bull.  Geol.  Soc.  of  Amer- 
ica, vol.  12,  1901,  p.  313. 

Grout,  F.  F.,  Contribution  to  the  Petrology  of  the  Keweenawan. 
Jour.  Geol.,  vol.  XVIII,  1910,  p.  633. 


STRUCTURE. 


89 


"Fault,  and  the  folds  within  the  Lake  Superior  synclinorium 
south  of  Ashland. 

Douglas  Fault.  The  exposures  of  the  great  fault  along  the 
northern  edge  of  the  Douglas  or  South  Range  have  been  de- 
scribed in  detail  in  the  last  chapter — the  conclusion  being  there 
reached  that  the  displacement  is  in  large  part  later  than  the 
deposition  of  the  sandstones,  although  movement  may  have 
taken  place  before  or  during  their  formation.  The  fault  plane 
dips  to  the  south  at  angles  varying  from  38°  to  about  60°, 
and  the  south  side  is  raised  relatively  to  the  north  side,  tliis 
fact  showing  it  to  be  a  thrust  fault.  Its  origin  is  a  broken  anti- 
cline, as  shown  by  the  overturned  fold  of  sandstone  thrown  up  at 
•one  locality,  and  apparently  it  is  allied  in  point  of  age  with  the 
period  of  Keweenawan  folding.  The  displacement  on  this  fault 
must  be  enormous,  over  three  thousand  feet  being  known  at  one 
locality.  This  can  only  be  a  fraction  "of  the  total,  which  must  be 
equivalent  to  the  sum  of  the  thickness  of  the  traps  above  the  hori- 
zon at  which  the  fault  occurs  and  of  the  sandstones.  The  former 
rocks  were  estimated  by  Sweet1  to  be  at  least  36,000  feet  thick, 
above  the  lowest  horizon  faulted  up,  provided  that  unknown  faults 
have  not  duplicated  the  exposures.  It  seems  probable  that  from 
4,000  to  possibly  15,000  feet  of  sediments  overlie  the  traps  (see 
structure  sections  on  general  map)  in  the  vicinity  of  Superior. 
Since  the  displacement  along  the  fault  plane  is  greater  than  the 
stratigraphic  thickness  between  the  horizons  on  each  side  of  the 
fault,  a  throw  of  from  six  to  twelve,  miles  is  estimated.  This 
figure  is  truly  enormous,  but  is  no  greater  than  the  absolutely 
^proven  displacements  of  many  thrust  faults.  The  shortening 
represented  by  the  folds  between  Madeline  Island  and  the  Peno- 
kee  Range  is  computed  from  structure  sections  E-F  and  J-K 
to  be  at  least  five  miles,  agreeing  clcsely  with  the  lower  estimate 
given  for  the  fault. 

In  its  course  (see  general  map  in  pocket),  the  fault  does  not 
exactly  follow  the  northeast  strike  of  the  traps  and  sandstones, 
but  turns  in  a  zigzag  line  in  a  general  E-NE  direction,  thus 
cutting  across  the  strike  of  both  series.  Following  it  to  the 
southwest,  the  fault  thus  progressively  brings  older  sandstones 
in  contact  with  younger  traps. 


i  Sweet,  E.  T.,  Geol.  of  Wis.,  1873-9,  vol.  Ill,  p.  338. 


90 


STRUCTURE. 


The  Douglas  fault  does  not  pass  through  the  Apostle  Islands, 
but  appears  to  die  out  into  a  fold  which  in  turn  becomes  gentler 
and  finally  flattens  out  beneath  the  drift-covered  area  of  the 
Bayfield  ridge.  The  dying  out  of  the  fault  is  to  be  correlated 
with  the  northeastward  pitch  of  the  minor  folds  (see  p.  92),  and 
the  general  broadening  of  the  synclinorium  in  northern  Ash- 
land County.  The  compressive  stress  which  to  the  west  was  re- 
lieved by  the  thrust  fault,  was  there  relieved  by  folding.  It  is 
very  probable  that  this  dying  out  is  accompanied  by  normal 
faulting  perpendicular  to  the  strike.  Such  dip  faults  are  known 
to  occur  at  some  of  the  angles  in  the  course  of  the  thrust  fault 
(see  p.  81).  As  indicated  by  the  topography,  the  fault  appears 
to  follow  a  nearly  straight  line  from  where  the  trap  outcrops 
on  Iron  River,  to  the  southwest,  where  the  Trap  Range  become?) 
ill  defined ;  and  finally,  in  the  vicinity  of  Maple,  in  Douglas 
County,  is  entirely  buried  beneath  the  Pleistocene  deposits. 
Where  exposed  on  Middle  River,  the  fault  has  a  strike  of  N.  65° 
W.,  thus  showing  that  there  is  a  reentrant  in  its  course  beneath 
this  unexposed  gap.  In  this  reentrant  is  found  the  great  over- 
turned fold  of  Middle  River  (see  p.  66).  This  fold  is  apparently 
a  local  feature  associated  with  the  change  in  direction,  but  un- 
fortunately the  exposures  on  Poplar  River  are  not  sufficient  to 
allow  its  eastern  extension  to  be  examined.  Cross  faulting  may 
also  occur. 

Plate  XIII,  p.  66,  represents  the  structure  of  the  rocks  exposed 
on  Middle  River,  to  the  north  of  the  fault;  its  general  features 
have  already  been  explained.  Jointing  in  the  sandstone  is 
best  developed  along  nearly  horizontal  planes  (Plate  XXI 
opposite).  In  some  cases  these  show  faulting,  the  upper  blocks 
having  moved  a  few  inches  to  the  north.  The  actual  junction 
with  the  trap  is  not  exposed,  but  is  associated  with  no  marked 
breaking  or  crushing  of  the  sandstone.  The  trap  is.  however, 
considerably  brecciated.  The  thickness  of  strata  of  sandstone 
involved  in  the  fold  shows  that  there  has  been  at  least  3.000 
feet  of  movement  on  the  fault  at  this  point. 

Between  Middle  and  Amnicon  Rivers,  the  fault  takes  a  course 
nearly  due  west.  Just  at  the  crossing  of  the  latter  stream  it 
resumes  a  southwesterly  direction.  This  exposure  is  described 
in  detail  on  pp.  77-79.    It  would  appear  that  the  confused  fault- 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.       Bulletin  No.  XXV,  Tlate  XXI. 


Middle  River,  Douglas  County. 


A.  Vertical  beds  of  red  reldspathic  sandstone  of  Orienta  formation,  showing 
horizontal  joints  formerly  mistaken  for  bedding.  Just  north  of  bridge  on  south 
line  of  Sec.  24,  T.  48,  R.  12  W. 


B.  Overturned  beds  just  south  of  the  bridge,  from  which  A  was  taken. 


STRUCTURE. 


91 


ing  along  planes  essentially  parallel  to  the  main  displacement, 
is  due  to  this  change  in  direction.  Because  of  this,  the  st na- 
tions seen  on  the  sandstone  (see  p.  78)  have  little  weight  in  dis- 
closing the  history  of  the  displacement. 

Southwest  of  Amnicon  River,  the  fault  follows  the  more  or 
less  marked  escarpment  of  the  trap  range,  to  where  it  crosses 
Black  River.  The  only  good  exposure  of  this  portion,  on  Cop- 
per Creek,  shows  that  the  plane  of  movement  dips  about  60° 
to  the  southeast.  The  sandstone  is  sharply  flexed  and  sheared 
for  less  than  50  feet  from  the  junction. 

Another  reentrant  occurs  at  the  falls  of  Black  River  (Plate 
XIX,  p.  80).  This  is  marked  by  normal  dip-faulting,  as  well  as 
by  faulting  in  the  sandstone,  parallel  to  the  main  plane  of  dis- 
placement, which  is  seen  to  dip  about  50°  to  the  south.  The 
trap  is  intensely  breeciated.  A  small  normal  fault  of  E-W 
strike  is  found  in  the  sandstone  still  farther  to  the  north. 

West  of  Black  River,  only  slight  bends  interrupt  the  south- 
westerly course  of  the  fault.  The  only  known  exposure  in  Wis- 
consin (see  p.  81)  shows  a  sharp  flexure  of  the  sandstone  and 
considerable  brecciation  of  both  formations. 

In  Minnesota,  Hall1  has  shown  that  the  great  fault  extends 
far  to  the  southwest,  nearly  to  St.  Paul,  but  its  age  has  not  been 
satisfactorily  determined. 

North  Coast  Fault.  For  various  reasons,  the  evidence  being 
mainly  physiographic,  it  has  long  been  thought  that  the  abrupt 
descent  from  the  nearly  level  uplands  of  Minnesota  to  the  deep- 
est part  of  Lake  Superior  was  marked  by  a  fault.2  Moreover,  at 
Superior,  deep  wells  show  a  considerable  thickness  of  shale, 
across  the  river  from  the  high  trap  hills.  The  dip  of  the  for- 
mations here  is  not  known,  however,  so  that  it  might  readily  be 
steep  enough  to  carry  the  sediments  over  the  traps. 

St.  Louis  River.  On  St.  Louis  River  there  is  observable  a 
dip  of  6°  to  10°  to  the  southeast,  together  with  a  complex  system 
of  normal  faults  (see  Plate  XV,  p.  70).    These  faults  are  un- 


1  Hall,  C.  W.,  Keweenawan  of  Eastern  Minnesota,  Bull.  Geol.  Soc.  of 
America,  vol.  12,  1901,  p.  313. 

2  Martin,  L.,  The  Geology  of  the  Lake  Superior  Region,  Mon.  U.  S. 
Geol.  Survey,  vol.  LII,  p.  112. 


92 


STRUCTURE. 


usually  well  exposed  (see  Plate  XXIII,  B,  p.  94),  so  that  the  ex- 
act plane  of  movement  can  usually  be  observed.  This  varies  in 
dip  from  vertical  to  about  60°  toward  the  downthrow  side.  This 
displacement  varies  from  a  few  inches  up  to  about  40  feet ;  the 
fault  shown  in  Plate  XXIII,  B,  has  a  throw  of  about  14  feet.  The 
strike  of  most  of  the  faults  averages  about  N.  35°  W.,  but  a  few 
have  a  nearly  E-W  direction.  Occasionally,  slickensides  occur; 
these  indicate  more  or  less  of  a  horizontal  component  to  the  mo- 
tion. As  already  mentioned  (p.  87),  it  appears  necessary  to  as- 
sume the  existence  of  a  fault  between  the  sandstones  of  Mission 
Creek  and  the  trap  bluffs  at  Short  Line  Park ;  but  the  drill  record 
(see  p.  85)  near  the  latter  locality  is  so  ambiguous  as  to  afford 
small  help  in  locating  the  displacement. 

Folds  Near  Ashland.  Beneath  the  eastern  plain  southeast 
of  Ashland,  occur  the  most  interesting  structural  features  of  the 
district.  Unfortunately,  however,  few  outcrops  exist,  so  that 
much  of  the  structure  remains  obscure.  But  sufficient  evidence 
has  been  discovered  to  show  that  we  have  to  deal  with  the  south 
half  of  an  asymetric  synclinorium,  in  which  the  southward  dips 
are  comparatively  gentle  while  the  northerly  dips  are  steep. 
The  southern  side  of  the  synclinorium  carries  more  minor  folds 
than  the  northern  (see  structure  sections  on  large  map).  These 
minor  folds  appear  to  pitch  to  the  east  and  northeast. 

The  strata  of  the  Apostle  Islands  represent  the  gently-dip- 
ping north  limb  of  the  great  depression,  while  the  faulted  anti- 
cline of  the  Douglas  trap  range  is  a  subordinate  eastward-pitch- 
ing fold  on  this  limb.  If  the  map  were  continued  farther  south, 
we  should  find  (see  Atlas  Plate  XXII,  Geology  of  Wisconsin, 
1873-79)  that  as  the  axis  of  this  great  Lake  Superior  synclin- 
orium passes  inland  near  Chequamegon  Bay,  it  suffers  a  rather 
sudden  bend  from  its  northeast-southwest  direction  to  a  course 
slightly  north  of  west.  Farther  to  the  west,  however,  as  shown 
on  the  map  by  the  line  indicating  the  probable  course  of  the 
synclinal  axis,  it  resumes  its  usual  southwesterly  direction. 

In  the  vicinity  of  Oronto  Bay  are  good  exposures  of  the 
southern  limb  of  the  main  fold.  Here  the  strike  averages  N.  53° 
E.  with  a  northwesterly  dip  of  45°  to  90°,  the  average  being 
about  65°.  Minor  undulations  are  not  common,  nor  are  joints 
especially  numerous  (see  table  on  p.  96).    Small  dip  faults 


Wisconsin  Geol.  and  Nat.  Hist.  Survey.       Bulletin  No.  XXV,  Plate  XXII. 


B.  General  view,  looking  south,  of  falls  of  Amnicon  River,  at  contact  of  traps 
and  Orienta  sandstone.  The  falls  are  just  on  the  fault  (see  Plate  XVIII,  p.  76, 
and  Plate  XVIIIa,  p.  78). 


STRUCTURE. 


93 


occur  in  places,  with  striae  showing  that  the  movement  has  been 
mainly  horizontal;  the  displacements  are  apparently  not  over 
45  feet.  Slickensides  also  occur  on  some  of  the  beds,  while 
inclined  fractures  dipping  toward  the  northwest  combine  to 
give  an  impression  that  there  has  been  strike  faulting  with  the 
down-throw  towards  the  lake.  Inclined  fractures  striking  par- 
allel to  the  dip  also  occur,  but  the  details  were  not  worked  out. 

Northwest  of  Oronto  Bay,  the  first  minor  fold  of  the  synclinor- 
ium  has  its  crest  at  the  apex  of  Clinton  Point.  This  locality  is 
figured  in  detail  in  Plate  IX,  p.  54.  The  beds  which  dip  to  the 
southeast  are  submerged,  hence  are  only  visible  when  the  water 
is  clear  and  calm,  and  then  are  seen  at  their  best  from  the  top 
of  the  bank.  Most  of  the  exposures  to  the  west  are  almost 
aswash,  so  that  it  is  not  surprising  that  former  visitors  have 
misinterpreted  the  structure  (see  p.  15).  The  inland  continu- 
ation of  the  fold  is  unknown,  the  deep  well  at  Birch  not  having- 
struck  rock  at  a  depth  of  300  feet;  but  apparently  the  anti- 
cline merges  into  the  south  limb  of  the  main  fold,  as  shown  on 
the  map. 

Close  to  the  north  side  of  the  anticline,  runs  the  axis  of  a 
syncline,  which  must  lie  between  it  and  the  southeasterly-dip- 
ping rocks  on  Bad  and  White  rivers.  At  the  former  locality 
the  dip  varies  from  27°  to  55°  to  the  southeast  with  a  strike 
of  about  N.  50°  E ;  at  the  other,  the  strike  is  about  the  same,  with 
a  dip  averaging  about  25°.  The  rocks  have  not  been  greatly 
affected  by  the  folding.  Joints  are  not  abundant,  and  most  of 
them  follow  the  strike  (see  table). 

Passing  again  to  the  northwest,  the  next  known  exposures  are 
those  on  the  South  Fork  of  Fish  Creek,  near  Ashland.  Here 
the  strike  averages  N.  85°  W.,  corresponding  to  that  of  the 
rocks  of  the  south  limb  of  the  synclinorium  farther  to  the  south, 
while  the  dip  is  northerly  at  angles  varying  from  70°  to  90°, 
the  inclination  lessening  towards  the  north  (see  Plates  VIIIr 
p.  52,  XI  a,  p.  62,  XI  b,  p.  64,  XI  c,  p.  64).  There  is  no  repeti- 
tion of  beds  by  close  folding.  Horizontal  or  slightly  inclined 
joints  are  most  common.  On  some  of  these  there  has  been  dif- 
ferential movement,  so  that  the  upper  side  has  moved  north. 
The  maximum  displacement  noted  was  about  four  feet.  A  small 
thrust  fault,  dipping  20°  S.,  was  observed,  but  there  was  no  evi- 


94 


STRUCTURE. 


dence  of  a  displacement  of  more  than  15  to  20  feet  (see  Plate 
XI  c,  A,  p.  62).  The  strike  of  the  fault  is  the  same  as  that  of 
the  beds. 

Between  the  north-dipping  rocks  of  Fish  Creek  and  the  ex- 
posures on  White  River,  five  miles  to  the  southeast,  there  must 
exist  an  anticline  which  may  possibly  be  faulted  like  that  of  the 
Douglas  Range.  It  is  difficult  to  decide  on  which  side  of  the 
center  of  the  synclinorium  this  axis  lies;  but  the  evidence  ap- 
pears to  favor  the  view  shown  on  the  map — that  it  is  on  the 
southern  side,  merging  with  the  main  south  limb  near  the  bend 
to  the  southwest.  On  account  of  the  absolute  lack  of  exposures 
west  and  northwest  of  Fish  Creek,  the  distribution  of  the  forma- 
tions shown  on  the  map  is  mainly  hypothetical. 

Structure  of  the  Bayfield  Group.  The  strata  of  the  Hay- 
field  group  are  in  general  but  slightly  inclined.  The  dip  varies 
from  nothing  up  to  a  maximum  of  about  5  degrees,  except  where 
the  strata  have  been  affected  by  the  Douglas  fault,  and  towards 
the  edges  of  the  synclinorium,  on  Fish  Creek  and  St.  Louis 
River,  where  greater  dips  are  found.  In  spite  of  the  fact  that 
this  dip  is  higher  than  the  average  for  the  flat-lying  rocks  in 
southern  Wisconsin,  joints  are  not  as  abundant  as  in  the  latter 
region.  In  most  cases  the  fractures  are  irregular  and  often  end 
at  bedding  planes  (see  Plate  IV,  B,  p.  30).  For  the  most  part, 
only  well-defined  fractures  were  measured  by  the  writer,  since 
the  minor  ones  are  often  curved  or  run  in  such  a  variety  of  direc- 
tions that  measurements  are  meaningless. 

The  accompanying  table  and  diagram  show  that  the  best  de- 
veloped joints  approximate  an  E-W  direction ;  next  in  impor- 
tance follow  those  which  strike  a  little  east  of  north,  while  north- 
west and  northeast  joints  are  occasionally  noted.  It  will  be  seen 
that  there  Is  little  relation  to  the  direction  of  the  strike  and  dip 
of  the  bedding,  or  to  the  main  lineaments  of  the  country.  Many 
of  the  E-W  joints  are  inclined,  usually  at  a  steep  angle  to  the 
north. 

Occasionally,  beds  are  found  that  are  much  more  fractured 
than  those  above  or  below.  An  instance  of  this  is  found  near 
the  northeast  corner  of  Oak  Island,  where  a  shaley  bed  a  few 
feet  in  thickness  is  cut  into  small  slabs  and  sometimes  long  sliv- 
ers, by  a  set  of  N-S  and  E-W  joints.    On  Point  Detour,  Poplar 


STRUCTURE. 


95 


River,  and  North  Twin  Island  occur  other  sheared  layers  of 
sandstone.  The  fragments  are  usually  subangular  and  consist 
of  the  adjacent  sandstone,  but  they  are  always  much  weathered. 
They  much  resemble  conglomerate  on  the  weathered  surface, 
but  lack  a  decisively  sedimentary  character ;  while  the  layers 
often  pinch  out  or  run  into  irregularly  broken  rock.  Presum- 
ably these  phenomena  are  due  to  shearing  and  in  part  to  con- 
cretions of  iron  (cf.  p.  31). 

Age  of  the  Deformation.  There  is  no  direct  means  of  de- 
termining the  age  of  the  deformation  of  the  sandstone  groups. 
It  will  be  pointed  out,  however  (see  p.  101,  in  the  consideration 
of  their  origin,  that  it  is  quite  probable  that  earth  movements 
went  on  simultaneously  with  the  deposition  of  .sediments  of  the 
Oronto  group.  It  is  also  probable  that  the  movements  which 
formed  the  Douglas  fault,  continued  throughout  the  period  of 
deposition  of  the  Bayfield  group,  for  there  has  been  a  great 
amount  of  displacement  since  its  beds  were  hardened.  The 
Orienta  sandstone,  a  member  of  the  Bayfield  group,  is  involved 
in  the  general  regional  folding  in  the  vicinity  of  Ashland. 
In  many  places  it  would  appear  from  the  lack  of  secondary 
structures  due  to  folding  (see  p.  92),  that  the  deformation  took 
place  before  the  rocks  were  entirely  indurated.  This  supposi- 
tion agrees  with  the  scarcity  of  joints  throughout  most  of  the 
area.  Many  faults,  although  formed  after  hardening,  are  now 
entirely  recemented,  while  secondary  fractures  unrelated  to 
folding  are  quite  common.  There  is,  however,  no  evidence  of 
any  marked  deformation  since  that  which  produced  the  folds 
and  faults.  This  deformation  appears  to  have  continued 
throughout  all  of  the  Keweenawan  period. 

Origin  of  West  End  of  Lake  Superior.  The  main  body  of 
Lake  Superior  occupies  a  great  structural  as  well  as  topographic 
depression.  It  would  appear  probable  that  the  deformation  of 
the  rocks  took  place  mainly  during  and  shortly  after  the  Ke- 
weenawan period,  and  that  the  present  depth  of  the  topographic 
basin,  slight  compared  with  its  width,  is  due  to  subsequent  ero- 
sion (by  what  agency  is  unimportant  for  this  discussion)  of  the 
relatively  soft  Upper  Keweenawan  sediments  that  occupied  its 
center.  Turning  to  the  western  portion  of  the  lake,  especially 
westward  of  the  Apostle  Islands,  -there  is  found  little  evidence 


STRUCTURE. 


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98 


STRUCTURE. 


of  a  structural  origin  of  the  present  topography,  although  the 
rock  fractures  of  the  Oronto  Bay  region  do  indicate  a  depression 
of  the  lake  bed  since  the  completion  of  the  folding.  Indeed,  the 
lake  does  not  extend  so  far  up  the  main  syncline  south  of  the 
Bayfield  Peninsula  as  it  does  north  of  the  Douglas  Kange  toward 
Superior.  On  the  south  side  of  this  great  western  extension 
of  the  lake,  we  find  no  vestige  of  a  structural  origin,  for  the 
sandstone  universally  dips  away  from  the  lake.1  (See  structure 
sections  on  general  map,  in  pocket.) 

The  explanation  must  lie  in  differential  erosion.  We  can 
clearly  discern  that  the  Bayfield  Peninsula  must  owe  its  origin 
primarily  to  different  causes  than  the  trap  ridge  of  Keweenaw 
Point,  which  it  resembles  in  outline.  It  may  be  supposed  that 
the  influence  of  the  soft  shales  of  the  Amnicon  formation  is 
responsible  for  the  development  of  the  Superior-Duluth  arm  of 
Lake  Superior.  A  study  of  the  depth  of  the  water  shows  that 
the  deeper  part,  which  is  not  over  900  feet,  is  confined  to  the 
neighborhood  of  the  north  coast,  where  this  formation  is  be- 
lieved to  outcrop  (see  p.  73).  At  Superior,  well  records  show 
that  this  ancient  valley  lies  upon  the  shales  next  to  the  foot  of 
the  Minnesota  trap  range.  It  is  known  to  have  been  eroded  at 
this  point  to  a  depth  of  over  500  feet  below  the  present  lake 
level.  In  the  case  of  the  Chequamegon  Bay  region,  the  struc- 
ture was  more  complex,  so  that  beds  of  varying  hardness  and  at- 
titude were  exposed  by  erosion.  Buried  valleys,  almost  as  deep 
as  those  at  Superior,  are  known  from  the  records  of  wells  south 
of  Mason  and  in  Ashland  County.2 

The  Bayfield  Peninsula,  then,  is  a  ridge  of  flat-lying,  com- 
paratively resistant  sandstone,  left  as  an  erosion  remnant  be- 
tween two  areas  mainly  composed  of  shales  and  soft  arkose.  The 
outline  of  the  islands  is  approximately  that  of  the  pre-glacial 
hills  into  which  this  ridge  was  cut.  Some  of  the  ancient  valleys 
between  them  (as  east  of  Outer  Island)  appear  to  have  es- 
caped filling  by  the  glaciers  which  deposited  the  huge  interlo- 

1  Owen  correctly  observed  this  feature.  Geol.  Survey  of  Wis.,  etc., 
p.  270. 

2  These  records  and  many  others  are  on  file  in  the  office  of  this  Sur- 
vey. 


STRUCTURE.  99 

bate  moraine  upon  this  dividing  ridge,  thus  giving  to  it  its  pres- 
ent height.  That  the  erosion  of  this  part  of  the  Lake  Superior 
basin  was  the  work  of  streams,  rather  than  of  ice,  therefore  ap- 
pears most  probable. 


100 


CONCLUSIONS. 


CHAPTER  VIII 


CONCLUSIONS 


General  Statement.  No  fossils  have  been,  or  seem  likely  to 
be,  discovered  in  either  the  Bayfield  or  Oronto  groups  of  sedi- 
ments, by  means  of  which  they  may  be  assigned  to  a  definite  geo- 
logic period.  They  must  therefore  be  correlated  on  the  basis  of 
lithologic  characters,  origin,  and  general  stratigraphic  and  phy- 
siographic relations. 

Summary  of  Lithologic  Characters.  The  sandstones  and 
shales  of  the  Wisconsin  coast  of  Lake  Superior  comprise  an 
enormous  thickness  of  sediments,  amounting  possibly  to  nearly 
25,000  feet.  In  composition  they  show  a  progressive  change, 
with  but  minor  alternations,  from  sediments  composed  of  poorly 
assorted  and  almost  unaltered  fragments  of  igneous  rocks,  to 
dominantly  siliceous  sandstone,  which  represents  a  marked  de- 
gree of  weathering  and  assortment  of  the  original  material. 

The  greater  part  of  the  lower,  or  Oronto  group,  may  be 
placed  in  the  first  class.  It  is  composed  of  debris  of  igneous 
rocks  winch  usually  was  but  poorly  assorted,  and  little  weath- 
ered or  worn  before  deposition.  In  the  Bayfield  group,  the  forces 
of  decomposition  and  sorting  had  greater  effect,  so  that  a  much 
greater  proportion  of  more  resistant  minerals  are  found.  The 
dominant  source  of  the  sediments,  moreover,  had  changed.  The 
material  of  the  older  group  was  mainly,  although  not  wholly, 
derived  from  the  Middle  Keweenawan  traps,  while  the  siliceous 
sands  and  orthoclase  feldspars  of  the  Bayfield  group  represent 
the  debris  of  older  sediments,  granites,  gneisses,  and  schist?. 
Both  groups  differ  from  the  older  sedimentary  series  of  the 


CONCLUSIONS. 


101 


»  Lake  Superior  region  in  containing,  so  far  as  known,  neither 
iron  formation  nor  distinct  pyroclastic  material. 
Comparison  with  Sandstones  of  Southern  Wisconsin.  The 

differences  of  the  rocks  of  the  Oronto  group  from  the  sand- 
stones of  southern  Wisconsin  are  clearly  apparent.  The  Bay- 
field group,  although  in  some  horizons  much  like  the  southern 
rocks,  differs  in'  many  important  respects.  Its  color  is  usually 
some  shade  of  red;  while  the  southern  sandstones,  where  they 
contain  iron,  are  prevailingly  yellowish.  The  dominant  cement 
of  the  latter  rocks  is  calcium  carbonate,  and  this  is  almost  en- 
tirely absent  in  the  Bayfield  group,  its  place  being  'taken  by 
silica  and  iron  oxide.  The  sand  grains  are  almost  universally 
much  less  rounded,  and  the  secondary  enlargements  are  very  ir- 
regular. Nevertheless  they  are  more  indurated.  Much  more 
feldspar,  mica,  magnetite,  and  other  minerals  derived  from 
rather  basic  rocks  are  found.  Clay  pockets,  and  pebbly  bed- 
ding planes,  as  well  as  irregular  and  curved  bedding,  are  char- 
acteristic of  the  northern  sandstones.  But  little  clay  shale,  or 
clean  quartz  sandstone,  and  no  fossils,  occur  in  these  rocks.  All 
these  facts  point  to  different  conditions  of  origin,  as  well  as  a 
somewhat  different  source  of  material,  from  that  of  the  sand- 
stones of  the  southern  part  of  the  state. 

Origin  of  the  Sandstones.  The  facts  bearing  on  the  con- 
ditions of  origin  of  the  Oronto  group  are  numerous  and  almost 
indisputable.  That  it  is  a  non-marine  deposit  is  disclosed  by 
mud-cracks,  abundant  ripple  marks  (often  of  the  type  pro- 
duced by  currents),  rain  prints,  angular  sand  grains,  poor  as- 
sortment, absence  of  fossils,  and  by  channels  in  shale  beds  filled 
with  sandstone.  All  of  these  are  features  characteristic  of  stream 
deposits,  laid  down  by  shifting  and  variable  currents  of  water, 
probably,  but  not  necessarily,  under  desert  conditions.  The  flat 
clay  pockets  are  believed  to  be  associated  with  the  mud-cracks, 
being  dried  films  of  clay  broken  up  and  then  buried  in  the  sands. 
Another  feature  of  fluviatile  deposition  is  the  abundant  and  ir- 
regular cross-bedding,  dipping  in  various  directions.  The  exact 
origin  of  the  light-colored  spots,  so  conspicuous  in  many  locali- 
ties, is  unknown;  until  this  is  determined  by  chemical  work, 
little  can  be  concluded  from  the  color  of  the  rocks.  They  may 
be  due  to  particles  of  either  organic  matter  or  iron  pyrite.  The 


102 


CONCLUSIONS. 


prevailing  red  color  is  generally  believed  to  represent  aridity  at 
the  time  of  deposition.  Taken  in  connection  with  the  absence  of 
fossils,  it  certainly  does  denote  a  scarcity  of  life,  the  remains  of 
which  would  have  bleached  the  ferric  oxide ;  but  as  iron  was  so 
abundant  in  the  traps  from  whose  debris  the  sediments  were 
built  up,  this  conclusion  is  rendered  doubtful.  Apparently,  con- 
ditions were  favorable  to  the  oxidation,  but  not  to  the  chemical 
concentration  of  iron,  the  magnetite  beds  being  the  result  of 
purely  mechanical  processes.  Likewise  conditions  were  unfavor- 
able for  the  chemical  concentration  of  copper  derived  from  the 
traps.  The  salty  water  often  found  in  the  rocks  of  the  Oronto 
group  is  without  significance,  since  both  marine  and  non-marine 
sediments  are  salty. 

Passing  to  the  overlying  Bayfield  group,  we  again  find  nearly 
all  of  the  features  of  terrestrial  deposits  mentioned  above.  Nat- 
urally mud  cracks  are  not  as  common  as  in  the  more  shaley 
rocks  of  the  older  group,  but  are  occasionally  found  at  almost 
all  horizons.  The  flat  clay  pockets  and  eroded  channels  are 
abundant,  but  the  latter  differ  in  being  often  cut  in  sandstone 
and  filled  with  shaley  rock.  Kain  prints  were  not  noted.  No 
distinct  evidences  of  wind  action  were  discovered,  although  it 
is  possible  that  some  of  the  peculiar  cross-bedding  may  be  of 
dune  origin.  The  angular  character  of  the  sand  grains,  how- 
ever, does  not  favor  such  an  hypothesis.  Neither  can  any  defi- 
nite conclusion  be  drawn  from  the  ferric  oxide  which  gives  the 
predominant  color.  It  has  been  so  thoroughly  redistributed  by 
the  action  of  ground  water  that  its  original  state  is  a  matter  of 
doubt.  All  that  can  be  said  is,  that  most  probably  it  was  origin- 
ally confined  to  the  finer  grained  beds.  The  irregularly  scattered 
pebbles  —  concentrated  only  on  bedding  planes,  and  never 
forming  beds  of  any  thickness — are  also  believed  to  favor  the 
hypothesis  of  fluviatile  origin.  No  deposits  like  those  at  the 
foot  of  sea  cliffs  are  found  along  the  Douglas  fault,  although 
movement  probably  took  place  during  the  deposition  of  the  sand- 
stone. 

Age  of  the  Bayfield  Group.  The  age  of  the  Bayfield  group 
cannot  be  definitely  stated,  as  it  could  were  fossils  present.  It 
must  be  correlated  by  the  same  methods  that  are  used  with  the 
other  non-fossiliferous  series  of  the  Lake  Superior  region.  In 


CONCLUSIOXS. 


103 


the  past  it  has  been  considered  to  be  of  Cambrian  age:  first, 
because  of  the  supposed  striking  difference  in  degree  of  folding 
from  the  recognized  Upper  Keweenawan  sediments  (Oronto 
group)  ;  and  second,  because  of  its  likeness  to  the  eastern  Lake 
Superior  ( Jaeobsville)  sandstone  of  Michigan,  which  is  be- 
lieved to  be  Cambrian.  In  later  years  the  probable  areal  con- 
nection of  the  Bayfield  group  with  the  red  clastic  series  of  south- 
eastern Minnesota  has  been  appealed  to  in  order  to  prove  the 
Cambrian  age  of  the  entire  Keweenawan  series.  The  possibilities 
are,  then: 

1.  The  Bayfield  group  may  be  unconformable  upon  the  Or- 
onto group,  and  be  conformable  with  the  Potsdam  of  the  Miss- 
issippi valley.  It  may  be  either  the  same  thing  as  the  southern 
sandstone,  or  its  conformable  downward  extension. 

2.  The  Bayfield  group  may  be  unconformable  upon  the  Or- 
onto group,  and  be  unconformable  below  the  recognized  Cam- 
brian. It  would  then  belong  to  an  unknown  and  unrecognized 
period. 

3.  The  Bayfield  group  may  be  conformable  upon  the  Oronto 
group,  and  conformable  with  the  known  Cambrian.  This  Avould 
involve  the  assumption  that  the  period  of  KewTeenawan  defor- 
mation and  terrestrial  deposition  continued  until  the  advancing 
Cambrian  sea  reached  the  Lake  Superior  basin,  so  that  the  two 
types  of  deposition  merged  into  one  another. 

4.  The  Bayfield  group  may  be  conformable  upon  the  Oronto 
group,  and  unconformable  below  the  Cambrian.  The  time  rela- 
tions to  the  Cambrian  could  not  then  be  ascertained. 

The  writer  has  sought  to  demonstrate  in  the  foregoing  chapters 
that  there  is  no  reason  to  believe  in  the  existence  of  an  unconform- 
4fy  between  the  Oronto  and  Bayfield  groups.  Both  are  a  part 
of  the  Upper  Keweenawan,  none  of  the  sedimentary  rocks  of 
which  display  much  more  metamorphism  than  do  the  Paleozoics 
to  the  south.  The  Bayfield  group  has  moreover  been  shown  to 
be  horizontal,  merely  on  account  of  its  position  in  the  center  of 
the  Lake  Superior  synclinorium.  Locally  it  is  involved  in  the 
more  pronounced  Keweenawan  folds  and  faults,  thus  contrast- 
ing sharply  with  the  relatively  undisturbed  Cambrian  rocks  of 
southern  Wisconsin. 


104 


CONCLUSIONS. 


It  seems  highly  probable  that  the  red  clastic  series  which  fills 
the  continuation  of  the  Lake  Superior  syncline  beneath  the  Pale- 
ozoic rocks  of  Minnesota,  is  the  equivalent  of  part  or  all  of  the 
Upper  Keweenawan  rocks  of  Lake  Superior ;  although  they  may 
now  possess  no  areal  connection  with  them,  either  by  way  of  the 
main  syncline  or  by  way  of  the  strip  of  sandstone  adjacent  to 
the  Douglas  fault,  west  of  Lake  Superior.  The  known  thick- 
ness of  these  red  sediments  in  Minnesota  is  much  less  than  that 
of  the  equivalent  rocks  in  the  Chequamegon  Bay  region,  so  that 
it  may  be  that  they  represent  only  a  portion  of  the  series. 

The  areal  connection  of  the  Bayfield  group  with  the  lighter 
colored  quartz  sandstones  of  the  Kettle  River  region  appears 
highly  probable.  But  the  age  of  these  rocks  is  unknown,  since 
they  too  are  barren  of  fossils  and  are  separated  by  a  fault  from 
the  traps  which  intervene  between  them  and  the  known  Cam- 
brian of  the  St.  Croix  valley,  and  are  separated  by  a  drift-cov- 
ered interval  from  all  other  strata  of  known  age.  A  connection 
with  the  red  clastic  series,  is,  nevertheless,  possible. 

It  therefore  appears  that  the  Bayfield  group  is  much  more 
closely  allied  to  the  Upper  Keweenawan  than  to  the  Cambrian. 
Nevertheless,  we  must  recognize  the  possibility  that  it  may  have 
been  deposited  in  an  inland  basin,  in  part  at  least  contempor- 
aneously with  the  lower  parts  of  the  Cambrian  series,  and  may 
later  have  merged  into  the  marine  strata  when  the  advancing 
sea  entered  the  Lake  Superior  basin.  The  slight  degree  of  meta- 
morphism  exhibited  by  the  Keweenawan  sediments  as  compared 
with  that  of  the  older  rocks  of  the  region,  supports  this  view. 
However,  the  overlapping  of  the  upper  Cambrian  strata,  over 
the  red  sandstones  in  southeastern  Minnesota  appears  very  much 
like  an  unconformity.  Such  a  discordance  could  naturally  y,'< 
be  recognized  in  the  churn  drill  records  which  form  the  only 
source  of  information  regarding  these  deeply-buried  rocks. 

The  equivalence  of  the  Bayfield  group  with  the  Jacobsville 
sandstone  (" Eastern  sandstone")  of  Michigan  cannot  be  proved 
on  account  of  the  lack  of  areal  connection,  but  the  lithologic 
likeness  is  complete.  The  Jacobsville  is  believed  by  Lane  and 
Seaman  of  the  Michigan  Survey  to  be  conformable  beneath  the 
light-colored  sandstones  (Munising)  of  known  Cambrian  age 
(see  p.  16).    The  two  areas  of  sandstones  are  separated  by  a 


CONCLUSIONS. 


105 


wide  area  of  older  rocks  and  may  well  be  of  widely  different 
ages.  Therefore  none  of  the  results  of  this  study  should  be 
applied  to  the  question  of  the  relative  ages  of  the  Michigan 
formations. 

The  question  of  the  relation  of  the  Keweenawan  to  the  Cam- 
brian cannot  be  here  entered  upon.1  It  is  sufficient  to  say  that 
so  far  as  "Wisconsin  is  concerned,  there  is  no  reason  for  separat- 
ing the  Bayfield  group  from  the  Oronto  group,  the  upward  con- 
tinuation of  which  it  undoubtedly  is.  Therefore,  the  Bayfield 
group,  according  to  all  observations  we  could  make,  is  of  Upper 
Keweenawan  age. 

Summary  of  Geologic  History.  The  Huronian  formations 
of  the  western  end  of  Lake  Superior  were  brought  substantially 
to  their  present  condition  before  the  deposition  of  the  earliest 
Keweenawan  sediments.  Their  sandstones  had  become  indurat- 
ed to  quartzites,  their  shales  largely  metamorphosed  to  slates, 
while  the  iron  formations  had  been  greatly  weathered.  In  Wis- 
consin, however,  much  of  the  deformation  appears  to  belong  to 
the  same  period  as  that  of  the  Keweenawan.2 

The  first  Keweenawan  sediments  were  quartzose  sandstone  and 
conglomerate,  derived  from  the  erosion  of  these  older  rocks. 
After  a  slight  thickness  of  this  had  accumulated,  volcanic  ac- 
tivity commenced.  Lavas  of  varying  types  were  poured  out 
until  a  thickness  of  many  thousands  of  feet  had  been  built  up 
in  the  structural  basin  now  occupied  by  Lake  Superior.  Most 
of  these  flows  were  of  basic  composition,  and  none  show  the 
characteristics  of  submarine  deposition.  Interbedded  with  the 
igneous  rocks  are  layers  of  conglomerate  and  sandstone,  derived 
from  the  erosion  of  adjacent  flows.  These  are  mainly  composed 
of  debris  from  acid  rocks,  since  those  probably  formed  greater 
elevations  than  the  more  fluid  basic  varieties.  In  the  latter  part 
of  the  eruptive  period,  enormous  masses  of  gabbro  were  in- 
truded into  the  surface  flows. 

During  the  deposition  of  these  Keweenawan  igneous  rocks, 
folding  and  faulting  went  on.   In  the  pebbles  of  the  Outer  Con- 

1  For  a  fuller  discussion  see  Van  Hise,  C.  R.,  and  Leith,  C.  K.,  Geol- 
ogy of  the  Lake  Superior  Region,  Mon.  U.  S.  G.  S.,  vol.  LII,  1911,  pp. 
378-415. 

2  A  full  statement  of  these  facts  will  be  found  in  Ibid.,  p.  366. 


106 


CONCLUSIONS. 


glomerate,  just  above  the  highest  flow  of  the  series,  are  found 
representatives  of  all  the  older  rocks,  including  the  deep-seated 
intrusives.  This  plainly  indicates  that  tilting  and  erosion  pro- 
ceeded simultaneously  with  deposition  in  the  lower  parts  of  the 
great  structural  basin.  Although  the  lowermost  Keweenawan 
rocks  noAv  exposed  were  thus  not  subjected  to  the  weight  of  all 
the  strata  stratigraphically  above  them,  there  is  no  reason  to 
doubt  that  an  enormous  thickness  was  laid  down  in  the  middle 
of  the  Lake  Superior  syuclinorium. 

Oronto  Group.  Following  the  deposition  of  the  lava  flows, 
the  volcanic  activity  ceased  and  sedimentary  rocks  alone  were 
formed.  These  rocks,  like  those  inferbedded  with  the  traps,  were 
laid  down  by  the  streams  that  eroded  the  upturning  edges  of 
the  great  basin,  and  deposited  their  load  upon  the  floor  of  the 
depression  in  order  of  the  coarseness  of  the  particles.  The  same 
process  may  now  be  seen  going  on  in  the  enclosed  basins  of 
modern  mountains.  "Whether  or  not  standing  water  occupied 
any  of  the  syncline,  or  the  sea  entered,  is  unknown ;  for  it  should 
be  recognized  that  the  only  rocks  now  visible  are  those  that 
were  deposited  near  the  edges. 

A  comparison  with  modern  alluvial  fans,  shows  that  the  grade 
of  the  depositing  streams  probably  decreased  as  they  left  the 
mountains.  Near  the  foot  of  the  surrounding  elevations,  con- 
glomerate was  deposited  where  the  streams  just  began  to  spread 
out  and  deposit  the  coarsest  portion  of  their  load.  Farther  out, 
the  gradient  lessened  still  more,  and  sands  and  clays  were  de- 
posited on  a  slope  of  probably  less  than  a  hundred  feet  per 
mile.  Floods  and  shifting  of  channels,  however,  mixed  the  var- 
ious kinds  of  material,  giving  us  such  sharp  changes  as  between 
mud  and  gravel.  When  the  deposits  were  not  covered  by  water, 
mud  cracks  developed  and  hardened  sufficiently  to  be  preserved 
under  the  next  layer  of  sediment,  which  may  often  have  been 
blown  over  them  by  the  wind — although  there  is  no  recognizable 
evidence  that  any  large  dunes  existed.  At  other  times  the  shift- 
ing streams  formed  temporary  lakes,  in  which  ripple  marks  were 
formed  by  the  waves,  although  many  such  marks  appear  to  have 
been  formed  by  currents.  Again,  changes  in  the  currents  eroded 
troughs  in  previously-deposited  sediments.  These  were  later 
filled,  often  with  somewhat  coarser  material  than  that  below. 


CONCLUSIONS. 


107 


We  must,  therefore,  recognize  that  deposits  of  varying  litho- 
logic  character  were  formed  simultaneously,  so  that  such  forma- 
tions represent  not  periods  of  deposition  of  different  materials 
but  the  shifting  of  the  zones  of  deposition,  due  to  the  filling  up 
of  the  basin.  The  material  of  the  higher  beds  was  progressively 
more  and  more  weathered,  a  fact  to  be  correlated  not  only  with 
this  process  of  shifting  zones,  in  which  the  material  deposited 
farthest  from  its  source  was  better  weathered,  but  also  with  a 
very  probable  lessening  in  the  rate  of  erosion  and  transporta- 
tion, and  possibly  with  increase  of  vegetation  on  the  uplands — 
both  factors  favoring  chemical  decomposition. 

Further,  it  appears  quite  probable  that  as  time  went  on,  the 
soft  basic  traps  were  eroded  to  low  levels  and  covered  more  and 
more  by  the  spreading  sediments.  Thus  the  older  sediments, 
granites,  and  other  more  siliceous  rocks  furnished  a  relatively 
greater  portion  of  the  material  brought  down  by  the  streams.  It 
will  further  be  seen  that  the  sediments  thus  overlapped  uncon- 
formably  upon  the  previously-eroded  lower  slopes  of  the  trap 
mountains,  so  that  although  no  exposure  of  such  a  contact  is 
known,  one  may  yet  be  found ;  but  this  would  not  prove  that  the 
sandstone  was  much  younger  than  the  trap.1  As  the  Douglas 
fault  is  structurally  a  part  of  the  general  Keweenawan  deforma- 
tion, it  is  entirely  probable  that  along  it  more  or  less  movement 
may  have  taken  place  throughout  the  time  of  deposition  of  the 
sediments. 

Bayfield  Group.  No  stratigraphie  or  sharp  lithologic  break 
occurs  between  the  Oronto  and  Bayfield  groups  of  sandstones, 
so  that  no  cessation  of  deposition  or  radical  change  in  conditions 
could  have  occurred.  The  further  extension  of  the  processes  out- 
lined above,  brought  about  the  change  from  little-weathered  felds- 
pathic  sands  and  clays  to  fairly-clean  quartz  sands  with  very 
little  clay.  The  greater  abundance  of  acid  trap  and  quartzite 
pebbles  shows  that  as  time  went  on  those  rocks  furnished  more 
and  more  material.    The  red  coloration  and  peculiar  bedding, 

i  It  appears  probable  that  the  red  clastic  series  of  Southeastern  Minn- 
esota overlaps  the  traps  of  the  center  of  the  basin  upon  the  granitic 
rocks  of  both  sides  of  the  basin,  and  gradually  thins  out  between 
them  and  the  overlying  Paleozoics. 


108 


CONCLUSIONS. 


troughs,  and  so  forth,  are  all  found  in  the  Bayfield  group,  thus 
indicating  conditions  of  deposition  similar  to  those  which  pre- 
viously prevailed.  It  is  unwise,  however,  with  the  present  im- 
perfect knowledge  of  the  interpretation  of  different  types  of 
bedding,  to  attempt  to  state  what  parts  of  the  formations  are 
fluviatile  and  what  subaqueous.  There  is  little  evidence  that  any 
is  strictly  aeolian.  There  is  a  strong  probability,  however,  that 
the  Devils  Island  sandstone  differed  in  manner  of  deposition 
from  the  beds  above  and  below.  The  prevailing  dip  of  the  cross- 
bedding  indicates  a  northern  source  for  the  material,  while  the 
lighter  color  and  abundant  ripple  marks  may  be  indicative  of 
'a  subaqueous  origin.  There  is  insufficient  coarse  and  unweathered 
sediment  in  the  neighborhood  of  the  Douglas  fault  to  render 
it  certain  that  there  was  any  considerable  movement  on  that  dis- 
placement, with  the  necessarily  consequent  rapid  erosion,  during 
the  period  of  the  deposition  of  the  Bayfield  group.  However,  as 
deformation  continued,  so  that  there  has  been  over  3,000  feet  of 
movement  since  that  time,  it  is  not  impossible  that  faulting  took 
place  at  intervals.  The  date  of  the  latest  movement  cannot  be 
ascertained;  but  as  the  lower  part  of  the  Bayfield  group  was 
involved  in  the  Keweenawan  folds,  it  is  evident  that  the  deforma- 
tion continued  at  least  to  that  time. 

As  no  formations  older  than  the  Pleistocene  overlie  the  Bay- 
field group  in  Wisconsin,  we  cannot  ascertain  how  long  sedi- 
mentation continued.  Presumably  the  entire  Lake  Superior  basin 
was  filled  up,  thus  checking  the  erosion  of  the  surrounding  high- 
lands. "Whether  or  not  the  deposition  of  the  Bayfield  group 
merged  into  the  Cambrian,  when  the  sea  invaded  the  continent,  is 
unknown.  The  entire  Lake  Superior  region  was  doubtless  cov- 
ered by  Paleozoic  sediments,  which  have  since  been  almost  wholly 
worn  away.  It  may  thus  be  seen  that  the  basin  of  the  present 
lake,  as  distinct  from  the  structural  basin  of  the  Keweenawan 
rocks,  does  not  differ  essentially  in  origin  from  the  basins  of  the 
other  Great  Lakes  (see  p.  95). 

Summary  of  Canclusions.  The  Bayfield  group  of  sand- 
stones is  conformable  upon  the  recognized  Upper  Keweenawan 
sediments,  and  is  therefore  a  part  of  that  series. 

The  contact  of  the  Bayfield  group  with  the  Middle  Keweena- 
wan traps  is  along  a  thrust  fault,  on  which  great  movement  has 


CONCLUSIONS. 


109 


taken  place  since  the  deposition  of  the  sandstones.  It  is  prob- 
able, however,  that  as  this  fault  is  to  be  correlated  with  fold- 
ing in  which  the  Bayfield  group  participated,  that  some  move- 
ment took  place  during  its  deposition ;  but  that  such  unconform- 
ity if  it  exists,  does  not  represent  any  considerable  lapse  of 
time. 

Folding  and  probably  faulting  went  on  contemporaneously 
with  the  deposition  of  both  the  Oronto  and  Bayfield  groups. 
The  sediments  accumulated  in  the  sinking  middle  portion  of  the 
great  Lake  Superior  syncline,  while  the  edges  were  being  rela- 
tively upraised  and  eroded.  As  the  sediments  accumulated,  they 
overlapped  unconformably  upon  the  feet  of  the  surrounding 
elevations.  Such  unconformable  contacts  have  been  largely 
eroded  away,  but  may  yet  be  found.  The  relation  of  the  sand- 
stones to  the  traps  at  Duluth  may  be  of  this  character,  but  is 
probably  complicated  by  faulting. 

Both  the  Oronto  and  Bayfield  groups  of  sediments  are  largely 
if  not  wholly  of  non-marine  origin,  having  been  laid  down  by 
streams  in  an  enclosed  basin,  not  necessarily,  although  very 
likely,  under  desert  conditions  and  probably  in  part  under 
standing  water.  The  climatic  conditions  were  favorable  to  the 
oxidation  of  iron,  a  fact  denoting  a  scarcity  of  vegetation. 

The  age  of  the  Bayfield  group  cannot  be  determined  without 
determining  the  relation  to  the  Cambrian  of  the  Mississippi 
valley,  with  which  no  areal  connection  is  definitely  known.  It 
is  possible  that  non-marine  deposits  in  the  Lake  Superior  basin 
may  have  merged  into  the  marine  deposition  of  the  Cambrian 
sea. 


INDEX 


(Includes  Plates) 


Alluvial  fans,  106 
Analyses,  chemical, 

Bayfield  group,  28 

Oronto  group,  52 
See  particular  localities. 
Amnicon  formation, 

analyses,  52 

bedding,  fig.  of,  69. 

contact  with  Huronian,  87. 

defined,  50 

local  details,  50,  54,  64-69,  73,  74, 
76,  84,  86,  98.    See  particular  lo- 
calities, 
photomicrographs,  66,  72. 
thickness,  50. 
views  of,  64,  74,  94. 
See  Oronto  group. 
Amnicon  River, 

bedding,  fig.  of,  30 
geology,  43-44,  77-79,  90-91. 
joints,  96-97. 
maps,  77. 
mentioned,  44,  81. 
quarry,  43-45. 
structure,  90-91. 
views  on,  76,  78,  92. 
Apostle  Islands, 

described  9-11,  by  Collie  20,  by  Irv- 
ing 17. 

geology,  15,  17,  33,  35-42,  45,  88, 
90,  92, 

mentioned,  6,  12,  58,  95. 

structure,  15,  17,  92. 

view  of,  8. 
See    Bayfield    group,   and  particular 

formations  and  localities. 
Appleyard,  A.  E.,  aid  acknowledged,  4. 
Ashland, 

geology,  41,  57,  92-95. 

mentioned,  12,   13,  16,  49,  62,  89. 

well,  62,  65-66. 
Ashland  County, 

geology,  90.  98. 
See  particular  localities. 


Ashland  Junction, 

geology,  42,  62-65. 
See  Fish  Creek. 
Archean  rocks,  area,  7. 

mentioned,  57,  58. 

Bad  River, 

analyses  of  rocks,  52. . 

geology,  54,  58. 

mentioned,  56. 

joints,  96-97. 

structure,  93. 
Bark  Bay,  geology,  42. 
Bark  Point,  geology,  42. 
Barksdale,  well,  34. 
Basswood  Island, 

analysis  of  sandstone,  28. 

geology,  36. 

joints,  96-97. 

photomicrograph,  26. 

quarry,  46. 
Bayfield,  geology,  36. 

mentioned,  20. 
Bayfield  group, 

age.  102-105 

analyses,  28. 

bedding,  29-30,  107-108. 

character,  general,  100-101. 

clay-pockets,  32. 

compared  with  Cambrian,  101,  103. 

Oronto  group.  49. 
composition.  26-27. 
contact  with  traps,  75-87. 
correlation.  3,  14-15,  82.  84,  102- 

105.    108-109.   by   Irving  16-17, 

by  Winch  ell,  18-19. 
defined,  2,  25. 

economic  products,  26,  45-47. 
extent,  2.  25,  58. 
geologic  history,  107-109. 
iron-banding.  31. 
joints.  96-97. 
mentioned.    5.  48. 
metamorphism.  103-104. 


INDEX. 


Ill 


mini  cracks,  33 

relation  to  Oronto  group,  62,  73-74, 
84. 

ripple  marks,  39. 

source  of  material,  32,  100,  107. 

structure,  25,  88,  94-95,  103. 

subdivisions,  26. 

thickness,  26. 
See    Cambrian,    Chequamegon  sand- 
stone, Devils  Island  sandstone,  Ori- 

enta  sandstone,  Oronto  group,  anu 

particular  localities. 
Bayfield  Ridge, 

described,  6,  8-9,  by  Irving,  16. 

geology,   13.   33,   88,  90. 

mentioned   11,  12,  25. 

origin,  98-99. 

view  of,  8. 
Bayfield  Peninsula, 

See  Bayfield  Ridge 
Beaches  of  lake,  9-10,  11. 

raised,  8. 
See  Lake  Superior. 
Bear  Island,  geology,  38. 

mentioned,  9. 
Bedford  linestone,  46. 
Berkey,  C.  P.,  mentioned,  76. 
Big  Bay,  joints,  96-97. 
•Birch,  well,  93. 
Birge,  E.  A.,  mentioned,  4. 
Black  River,  map  of  falls  of,  80. 

geology.  44.  80-81,  91. 

mentioned,  58. 

joints,  96-97. 
Brownstone,  use  of,  45-47. 

occurance  of,  33,  45—46. 
Brule  River,  geology,  13,  39,  41,  43,  76. 

joints,  96-97. 
Buckley,  E.  R.,  cited,  21,  27,  28,  35,  36, 
37,  43,  44,  45. 

photomicrographs  by,  26,  44. 

Cambrian,  compared  with  Bayfield  and 
Oronto  groups,  101. 

in  Michigan,  3,  14-16,  25,  103-105  ; 
in  Minnesota,  20,  26,  49,  58,  84, 
103  :  in  Mississippi  valley,  15,  18, 
19,  82.  84  ;  in  St.  Croix  valley,  21, 
59,  104. 

relation  to  Bayfield  group,  82,  84, 

103,  104-105,  108-109. 
relation  to  Keweenawan,  2,  82,  105. 
relation  to  red  clastic  series,  59-61, 

104,  107. 

See  Bayfield    group  ;    Irving.   R.   D.  ; 
Winchell,  N.  II.  ;  .Tacobsville  sand- 


stone, Munising  sandstone,  Potsdam 

sandstone. 
Case,  E.  C,  cited,  6,  21. 
Caves,  sea,  10,  39. 

views.  40,  94. 
Chamberlin,  T.  C,  cited,  22.    See  Irving, 
R.  D. 

Chequamegon  Bay.  described,  12. 

geology,  65,  88,  98. 

mentioned,  25,  33,  34,  74,  104. 
Chequamegon  Point,  described,  12. 
Chequamegon  sandstone, 

analyses,  28. 

bedding,  1,  29. 

defined,  20,  33. 

economic  products,  45-47. 

extent,  33. 

general  section.  33. 

joints,  96-97. 

local  details,  34-38.    See  particular 
localities. 

mentioned,  43,  65. 

photomicrographs,  26. 

structure,  33. 

thickness,  33. 
See  Bayfield  group. 
Chippewa  Land  District,  18. 
Clastic  series,  rod.  of  "Minnesota, 

correlation,  20,  59-61,  84,  103-104, 

107. 

defined,  2,  59. 

described,  59-60. 

thickness,  59. 
Clay.  red.  i.  9.  10,  11,  13. 
Clay-pockets,  described,  32-33. 

in   Oronto   group,  53. 

significance  of,  101-102. 
Clinton  Point,  described  by  Irving,  15. 

geology.   18-19,   21,  55. 

joints.  96-97. 

map,  54. 

mentioned,  12. 

photomicrograph,  56. 

structure,  93. 
Collie.  G.  L.,  work,  20. 

cited.  6,  10,  12.  20.  22. 
Colwell,  J.  A.,  cited,  73. 
Copper,  19,  58,  102. 
Copper  Creek,  geology,  44,  80,  91. 

joints,  90-97. 

mentioned,  45 
Copper  Creek  beds   (of    Orienta  sand- 
stone), 42,  43,  44,  67. 
Copper  Range   (of    Ashland    and  Iron 
Counties),  see  Southern  Highland. 


112 


INDEX. 


Copper   Range    (of   Douglas   Co.),   see  1 

Douglas  Range. 
Cornucopia,  geology,  41. 

mentioned,  39. 
Cross  bedding,  Bayfield  group,  29-30. 
Devils  Island  sandstone,  40. 
Oronto  group,  53. 
significance  of,  101. 
used  to  determine  top  of  strata,  53, 
63,  64. 
See  particular  localities. 

Devils  Island,  caves,  10. 

geology,  33,  38. 

.-joints,  96-97. 
Devils  Island  sandstone, 

defined,  26,  38. 

extent,  38-39,  41,  58. 

mentioned,  32,  34,  43,  44. 

origin,  40,  108. 

thickness,  39. 

views  of,  40,  94. 
Douglas  fault, 

age,  81-84,  95,  107. 

deposits  near,  102,  108. 

described,  75-84,  88-91  :  by  Grant, 
20  ;  by  Hall,  20  ;  by  Winchell,  18. 

extent,  59-61,  88-91. 

maps  showing,  77,  80. 

mentioned,  21,  41,  94,  104. 

views  of,  76,  78,  92. 
See  particular  localities. 
Douglas  range. 

described,  7-8. 

geology,  13,  16-17,  75-81,  89-92. 

mentioned,  2,  11,  25,   41,  59,  58, 

87,  88,  94,  98. 
See  Douglas  fault. 
Drift,  glacial,  described,  1,       8,  10,  13. 
Duluth,  geology,  19,  84. 

maps  near,  8,  17. 

mentioned,  8,  11. 
Dunes,  evidence  of,  102,  106. 
D'i  Pont  Powder  Works,  well,  34. 

Eagle  Island,  analysis  of  sandstone,  28. 

geology,  42. 

joints,  96-97. 
East    Superior,    geology,  73. 
Eastern  Plain,  ' described,  12. 

geology,  49. 

mentioned,  7. 

view,  8. 

Eastern  Sandstone.   See  Jacobsville  sand- 
stone ;  Cambrian   (in  Michigan). 


Economic  products,  Bayfield  group,  45- 

47  ;  Oronto  group,  58. 
Edin,  C.  N.,  aid  acknowledged,  5,  45. 
Eileen  sandstone, 
defined,  50. 

economic  products,  58. 

local  details,  54-55. 

mentioned,  64. 

photomicrograph,  56. 

thickness,  50. 

views,  52. 
See   Oronto  group. 
Eileen,  Town  of,  geology,  54,  62-65. 

See  Pish  Creek. 
Erosion,  glacial,  13. 

post-glacial,  13. 

Falls,  water,  described,  7,  8,  54,  78, 
80-81,  91. 

views,  58,  78,  92. 
Faults. 

age,  95. 

diagram  of,  97. 

dip  faults,  90-91,  96-97. 

Douglas,  see  Douglas  fault. 

horizontal,  90,  93. 

Keweenaw  Point,  18. 

Montreal  River,  21,  50. 

North  coast,  88-89,  91. 

Oronto  Bay,  92-93. 

St.  Louis  River,  86-87,  91-92,  94. 

striations  on,  78,  92-93. 

table  of,  96. 

views,  74,  76,  78,  92,  94. 
See  particular  localities. 
Field  work,  method,  3 
time,  3. 

Fifield,  S.  S.,  aid  acknowledged,  4. 
Fish  Creek, 

bedding,  figs,  of,  53,  55. 

geology,  41,  42,  50,  54,  62-65,  73-74, 
93-94. 

maps,  62. 

magnetite  beds,  54,  58. 
mentioned,  5,  15,  25,  56. 
photomicrographs,  56,  66. 
structure,  93—94. 
view's,  52,  64. 
Folds.    See  Structure,  under  formations 
and  localities  ;  Lake  Superior  syncline. 
Foley,  W.,  aid  acknowledged,  5. 
Fond  du  Lac,  Minn.,  geology,  84-87. 
quarry,  46. 
photomicrograph,  44. 
See  St.  Louis  River ;  Mission  Creek ; 
Short  Line  Park. 


INDEX. 


113 


Foxboro,  well,  45. 
Freda  sandstone, 

analysis,  52. 

defined,  48-49. 

local  details,  55-56.    See  particular 

localities, 
structure,  92-93. 
thickness,  50. 
views,  58. 
See  Oronto  group. 
Fuller,  M.   L.,  cited;  see  Hall,  C.  W. 


Gabbro,  Keweenawan,  84-85,  105. 

described,  7. 
See  Southern  Highland. 
Good  Land  Co.,  mentioned,  5. 
Grant,  U.  S.,  aid  acknowledged,  4. 

cited,   19,  20,   22,  44,   66,   75,  76, 
77,  80,  81. 

view  by,  50. 

work,  19-20. 
Graveyard  Point,  See  Clinton  Point. 
Grout,  F.  F.,  aid  acknowledged,  4. 

cited,  21,  22,  45,  58,  88. 

work,  21. 
Ground  water,  work,  31-32,  102. 


Hall,  C.  W.,  cited,  20,  21,  22,  58,  59, 
60,  86,  88,  91. 

work,  20. 
Herbster,  geology,  40,  42. 

mentioned,  11. 

view  near,  30. 
Hermit  Island, 

analysis  of  sandstone,  28. 

geology,  36-37. 

joints,  96-97. 

quarry,  36-37. 
High  Bridge,  geology,   16,  19. 
Holyoke,  Minn.,  geology,  45. 
Hotchkiss,  W.  O.,  aid  acknowledged,  4. 
Houghton,  analysis  of  sandstone,  28. 

geology,  35. 

joints,  96-97. 

photomicrograph,  26. 

quarries,  33,  35,  46. 
Houghton  Point,  see  Houghton. 
Huronian  rocks, 

extent,  7,  57,  58. 

deformation,  105. 

described,  7,  73,  84-87. 

geologic  history,  105. 
See  St.  Louis  River. 


Iron,  oxidation  of,  102. 
source  of,  102. 
See  Bayfield  group  :  iron  banding,  Or- 
onto group. 
Iron  River,  geology,  43,  75,  90. 
Irving,  R.  D.,  cited,  6,  12,  15,  16,  17, 
22,   23,  27,   28,   33,  42,   50,  54,  55, 
56,  57,  58,  81,  88. 
work,  15-17. 

Jacobsville  sandstone,  correlation,  14- 
16,  103-105. 

relation  to  Bayfield  group,  103-105. 
See  Cambrian. 
Johnson,  .1.   E.   Jr.,   aid  acknowledged, 

4,  66. 
Joints,  diagram,  97. 
table,  96. 

See  particular  localities  and  forma- 
tions. 

Kettle   River,   geology,    58-59,  60-61, 
104. 

Keweenawan  period, 

age  of,   103,  105. 

geologic  history,  105. 
See  Traps,  also  particu'ar  localities. 
Keweenawan  rocks,  area,  7. 
Keweenaw  Point,  fault,  18. 

mentioned,  3,  21. 

origin,  98. 
See  Jacobsville  sandstone  ;  Cambrian. 
Krey,  J.,  cited,  6,  23. 

Lake  Duluth,  described,  13. 

See  Lake  Superior :  raised  beaches. 
Lake  St.  Croix,  Douglas  Co.,  mentioned, 

13. 

Lake  Superior,  origin  of,  108. 

origin  of  west  end,  95-99. 

raised  beaches,  8-13. 

tilting,  13. 

view  of  beach,  i. 
Lake    Superior    group    (of  Michigan), 
14-16,  25,  103-105. 

See  Jacobsville  sandstone ;  Cambrian. 
Lake  Superior  group    (of  Wisconsin), 

See  Bayfield  group. 
Lake  Superior  syncline, 

extent,  60,  88,  92,  104. 
folds  in,  88-89,  92-94. 
sedimentation  in,  103,  106-109. 
Lake  Superior  Iron  &  Chemical  Co., 
well,  65-66. 


♦ 


INDEX. 


114 

Lake  Survey.  See  U.  S.  Lake  Survey. 
Land  Survey.  See  U.  S.  Land  Survey. 
Lane,  A.  C,  aid  acknowledged,  4. 

cited,  21,  23,  48,  50,  55,  104. 

work,  21. 
Lang,  F.  N.,  aid  acknowledged,  4. 
Lapham,  I.  A.,  mentioned,  16. 
Launch,  used  in  survey, 

described,  3. 

view,  i. 
See  Field  work. 
Lehner,  V.,  cited,  52. 
Leith,  C.  K.,  aid  acknowledged,  4. 

cited.  12.  24.  105.    See  Van  Hise. 

mentioned,  21. 
Leverett,  F..  cited,  13,  23. 

work,  12. 
Little  Manitou  Island,  described,  9. 
Long  Island,  described.  12. 
Lost  creek,  geology,  39. 

Madeline  Island, 

analysis  of  sandstone,  28. 

described,  9,  10. 

geology,  35,  89. 

mentioned,  11. 
Magnetite  deposits,  27,  54. 

fig.  of,  53. 

origin,  102. 

value,  58. 

view,  i. 
Maple,  geology,  90. 
Maps  of  district,  described,  3. 
Marble  Point,  see  Clinton  Point. 
Martin,  L.,  cited,  6,  24,  91. 

mentioned,  21. 
Mason,  geology,  98. 

well,  55. 
Meads,  A.  D.,  cited,  23. 
Meinzer,  O.  E.,  cited,  see  Hall,  C.  W. 
Mendota  limestone,  60. 
Merrill,  J.  A.,  aid  acknowledged,  4,  73. 
Michigan,  geology,  see  Cambrian  ;  Jacobs- 
ville  sandstone ;  Munising  sandstone, 
and  particular  localities. 
Middle  River, 

analysis  of  shale,  52,  72. 

described  by  Grant,  20 ;  by  Sweet, 
16. 

geology,  41,  44,  52,  54,  62,  66-69, 

73-74,-  76,  83,  90. 
map,  66. 

mentioned,  43,  49. 
photomicrographs  of  rocks,  68,  72. 
structure,  66.  83.  90. 
views,  50,  74.  90. 


Minneapolis,  geology,  59. 

Minnesota,  geology,  see  Clastic  series; 
Cambrian  ;  formations  and  localities. 

Minnesota  Geological  and  Natural  His- 
tory Survey,  work,  17. 
Sec  Winchell,  N.  H. 

Minnesota  Point,  described,  12. 

Minnesota  range,  see  North  Range. 

Mission  Creek,    Minn.,    geology,  84-87, 
92. 

See  St.  Louis  River,  Fond  du  Lac. 
Montreal  River,  analysis  of  sandstone, 
52. 

geology,  18,  19,  21,  56-57. 

structure,  21,  50. 
Mud  cracks, 

mentioned,  33,  35,  52,  68. 

origin,    101-102,  106. 

Oronto  group,  53. 
Munising  sandstone  (of  Michigan),  104- 

105  ;  see  Cambrian. 
Musback,  F.  L.,  aid  acknowledged,  4. 

Xi  .mad.ti  River,  geology,  45. 
Nonesuch  formation 

analyses,  52. 

character,  51. 

defined,  48. 

economic  products,  58. 

local  details,  55. 

mentioned,  50. 

thickness,  51. 
See  Oronto  group. 
North    Coast  Fault,   see  Faults. 
North  Twin  Island,  geology,  38,  95. 
North  range. 

described,  8. 

geology,  88.  98. 

mentioned,  11. 

view,  8. 
Norwood.  J.  G.,  cited,  28. 

work,  14. 

Oak  Island,  described,  9. 

geology,  37,  94. 

joints,  96-97. 

mentioned,  11. 
Odanah,  mentioned,  12. 
Orienta,  geology,  43. 

quarry,  43,  45. 
See  Iron  River. 
Orienta  sandstone, 

analyses,  28. 

bedding.  29,  30. 

brown  stone,  45—46. 

defined.  26,  41. 


INDEX. 


115 


economic  products,  45-46. 
extent,  41. 
general  section,  41. 
joints,  96-97. 

local  details,  42-45,  62-67,  69-73  ; 
see  particular  localities. 

mentioned,  41,  55. 

photomicrographs,  44. 

structure,  95. 

thickness,  41. 

views,  30,  40,  90,  92. 
See  Bayfield  group. 
Oronto  Bay,  geology,  56. 

mentioned,  49. 

joints,  96-97. 

structure,  92-93,  98. 
See  Oronto  River. 
Oronto  group, 

age,  103. 

analyses,  52,  72. 

bedding,  53,  55. 

character,    general,    49,  100-102. 
compared  with  Bayfield  group,  49  ; 

with   Cambrian,  101. 
composition,  51. 

correlation,   73-74;  by  Irving,  16— 

17  :  by  Winchell,  18-19. 
defined,  2,  25,  48-49. 
economic  products,  58. 
extent,  49,  58. 

geologic  history,  106-107,  109. 

joints  and  faults,  96-97. 

local   details,   54-57,   62-67,  69-73, 

84.    See    particular  localities, 
mentioned,  25,  32. 
metamorphism,  104. 
mud  cracks,  53. 
origin,  101-102. 

relation  to  Bayfield  group,  62,  73- 
74,  84. 

salt  water,  58,  102. 

source  of  material,  51,  100,  107. 

structure,  88,  90-95. 

subdivisions,  50. 

thickness,  49-50. 
See   Bayfield    group  ;    Clastic  series, 

and  particular  formations. 
Oronto  River,  geology,  21,  56-57. 

mentioned,  15. 

view,  58. 
Outer  conglomerate, 

described,  57. 

mentioned,  48,  49. 

origin,  105-106. 

thickness,  51. 
See  Oronto  group. 


Outer  Island,  geology,  i,  37. 
mentioned,  9,  98. 
view,  i. 

Owen,  D.  D.,  cited,  14,  23,  38,  39,  42. 
work,  14-15. 

Paint  rock,  58. 

Paleozoic,  sec  Cambrian. 

Panic  of  1893,  effects  of,  46. 

Patterson's  well,  73. 

Pebbles,  significance  of,  32,  102. 
See  Bayfield  group. 

Penokee  Range,  described,  6-7  ;  by  Irv- 
ing, 15  ;  by  Whittlesey,  15. 

geology,  89. 
See  Southern  Highland. 

Photomicrographs,  see  list  of  illustra- 
tions, particular  formations,  and  lo- 
calities. 

Tikes  Quarry  (Bayfield  Co.),  geology, 
31,  35-36. 

joints,  96-97. 
Pine  Barrens,  described,  9. 

mentioned.  6,  11. 
See  Bayfield  Ridge. 
Pleistocene    deposits,    described,  13. 

See  Drift. 
Point  Detour,  geology,  38,  94-95. 
Poplar  River,  geology,  43,  90,  94-95. 

joints.  96-97. 
Port  Wing,  analysis  of  sandstone,  28. 

geology,  42,  44,  67. 

joints,  96-97. 

photomicrograph,  44. 

quarry,  42-46. 
Potato  River,  geology,  56-57. 
Potsdam  sandstone,  described,  60. 

Minnesota,  84. 

relation  to  Bayfield  group,  103  ;  to 
red  clastic  series,  59-61. 
Sec  Cambrian 
Pre-Keweenawan  rocks,  described,  57. 

Quarries,   described,   31,  35-37,  42-46, 
58. 

See  particular  localities. 
Quarry  industry,  causes  of  decline,  46, 
condition  in  1910,  46. 
future   of.  47. 

Rain  prints,  53,  71. 

significance,  101-102. 
Randall.  A.,  work,  14. 
Recent  deposits,  described,  13. 

See  Drift. 


116 


INDEX. 


Ripple  marks,  figs,  of,  40. 
origin,  39-40,  101,  106. 
used  to  determine  top  of  strata,  68, 
76. 

St.  Croix  valley,  geology,  15,  21,  59, 
88,  104. 

See  Cambrian  ;  Clastic  series. 
St.  Louis  Bay,  described,  12. 
St.  Louis  River,  bedding,  fig.  of,  69. 

described  by  Winchell,  17-19. 

geology,  13,  54,  62,  69-74,  84-87. 

mentioned,  45,  49,  94. 

photomicrographs,  44,  72. 

structure,  91-92. 

views,  74,  94. 
See  Short  Line  Park,  Fond  du  Lac, 

Mission  Creek. 
St.  Paul,  mentioned,  91. 
Salmo,  geology,  35. 

Salt  water,  found  in  wells,  58,  66,  73, 
85. 

significance  of,  102. 
See  Wells 
Sands,  lake,  10. 

glacial,  10-11,  13. 

magnetite,  i,  27,  54. 
Sand  Cut,  described,  12. 
Sand  grains,  shape  of,  101,  102. 

See  particular  formations, 
Sand  Island,  geology,  10,  39,  42. 

joints,  96-97. 

mentioned,  11. 

views,  30,  40. 
Sand  Point,  geology,  33. 
Schroeder,  John,  Lumber  Co., 

mentioned,  5. 
Seaman,  A.  E.,  cited,  see  Lane,  A.  C. 
Section  corners1,  condition  of,  3. 
Shearing,  in  Bayfield  Group,  94-95. 
Short  Line  Park,  Minn.,  drill  hole,  19, 
85-87. 

geology,  92. 

structure  sections,  86. 
See  St.  Louis  River,  Mission  Creek. 
Silver,  58. 

Silver  Creek,  geology,  15,  19. 
Siskowit  Point,   analysis  of  sandstone, 
28. 

bedding,  29. 

geology,  42. 
Siskowit  River,   geology,  39. 

joints,  96-97. 
Soils  Division,  work,  4,  12. 
Southern  Highland,  described,  6-7. 

geology  6-7,  13. 


mentioned,  12,  49. 
view,  8. 

South  Range,  described,  7-8. 
view,  8. 

See  Douglas  fault,    Douglas  Range, 

and  particular  localities. 
Spits,  sand,  10. 
Spotting,  origin  of,  101-102. 
Squaw  Bay,  caves,  10. 

geology,  39. 

views,  40,  94. 
Squaw  Point,  geology,  42. 
Stearns,  J.  S.,  Lumber  Co.,  mentioned, 
5. 

Stillwater,  Minn.,  drill  hole,  19,  60. 

geology,  59-60. 
Stockton  Island,  geology,  37. 

joints,  96-97. 

mentioned,  9,  10, 
Striae,  glacial,  43. 
Superior,  geology,  13,  73,  91,  98. 

mentioned,  11,  16. 

wells,  49,  62,  73. 
Superior  Bay,  described,  11-12. 
Sweet,  E.  T.,  cited,  6,  15,  16,  23,  28,  43, 
44,  45,  66,  76,  77,  80,  89. 
work,  15-16. 

Thomson  slate,  73,  85-87. 
sections  showing,  70,  86. 
See    St.    Louis    River :    Short  Line 
Park  ;  Huron ian. 
Toole,   E.   H.,    aid   acknowledged,  4. 
Townships   (does  not  include  localities 
otherwise  designated)  : 
T.  46,  R.  4  W.,  Sec.  6,  geology,  55, 
view,  58. 

  R.  15  W.,  Sec.  6.  geology,  45. 

T.  47,  R.  3  W..  Sec.  25,  geology,  54. 

 r.  4  w.,  Sec.  5,  geology,  66. 

Sec.  19,  geology,  57. 

 r.  5  w.,  Sees.  11.  14.  15,  geol- 
ogy, 62-65;  map,  62. 
Sees.  20.  21,  geology,  54. 

 ■  R.  13  W.,  Sec.  7,  geology,  44. 

  R.  14  W.,  Sec   7,  geology,  80. 

Sec.  21.  geology,  80-81. 
Sec.  29,  geology,  45,  81. 

T.  48,  R.  5  W.,  Sec.  23,  geology,  34. 

  R.  10  W.,  Sec.  30,  geology,  44, 

76. 

 r.  14  w..  Sec.  27,  geology,  45. 

 R.  16  W.,  Sec.  1.  view,  94. 

T.  49,  R.  14  W.,  Sec.  24.  geology. 
73. 


INDEX. 


Ill 


Traps,  Kewecnawan, 
area,  7-8. 
copper  in,  19. 
described,  57. 
thickness,  89. 
view,  74. 
See  particular  localities. 
Trap  ranges,  see  Douglas  Range ;  North 
Range. 

Turvill,  T.,  aid  acknowledged,  4. 

United  States,  Bureau  of  Soils,  work, 
12. 

Dept.  of  Agriculture,  cited,  12,  24. 
Geological     Survey,     aid  acknow- 
ledged, 34. 
Lake  Survey,  mentioned,  4. 
Land  Survey,  3-4. 
Treasury  Dept.,  mentioned,  14. 

Valleys,  drowned,  11. 

post  glacial,  11-13. 

pre-glacial,  13,  98-99. 
Van  Hise,  C.  R.,  cited,  12,  105'. 

mentioned,  76. 
See  Leith,  C.  K. 
Veins,  calcite,  53,  57. 

Wash'burn,  geology,  29,  35. 

joints,  96-97. 

structure,  39. 
Washurn  beds   (of  Chequamegon  sand- 
stone), 33-34. 
Wayman  Point,  geology,  65. 


Weidman,   S.,   aid  acknowledged,  4. 

cited,  58. 
Wells,  Ashland,  62,  65-66. 

Birch,  93. 

Foxboro,  45. 

Mason,  55. 

Short  Line  Park,  Minn.,  85-87. 
Stillwater,  Minn.,  60. 
Superior,  49,  62,  73,  91. 
Western  Plain,  described,  11-12. 
geology,  41. 
mentioned,  7,  25. 
view,  8. 

Western  sandstone,  2,  16,  17,  25. 
See  Bayfield  group. 

Western   sandstone    (of  Michigan),  de- 
fined, 48. 
See  Oronto  group. 

White  River,  analysis  of  sandstone,  52. 
geology,  55,  93-94. 
joints,  96-97. 
structure,  93-94. 
view,  58. 

White  River  Lumber  Co.,  well,  55. 
Whittlesey,  C,  cited,  15,  24. 

work  14,  15. 
Wilson  Island,  see  Hermit  -Island. 
Winchell,  N.  H.,  cited,  17,  19,  23-24,  59, 

70,  85  86. 

work,  17-19. 
Wind  action,  evidences  of,  102. 
Wisconsin  Point,  described,  12. 
Wood,  K.  T.,  aid  acknowledged,  3. 

York  Island,  geology,  38. 


UNIVERSITY  OF  ILLINOIS-URBANA 

557W75B  C001 
BULLETIN.  MADISON 
25  1912 


